11 chapter3 section3 chemical industry page137 192

Section 3

Chemical Industry

Process Flow

3-1 Ammonia

3-2 Caustic Soda

3-3 Naphtha Cracking

3-4 BTX

137

Chemical (Ammonia) : Production Process and Energy Saving Technology

Synthesis processGas refining processCO conversion processGrassification (reforming) process

Item No. Technology Item/Title

CA-PE-2 Heat exchanger type primary reformer for wasteheat recovery in ammonia production process

CA-ME-4 Installation of pre-reformer in ammonia reformingprocess

CA-ME-5 Primary reformer waste heat recovery unit forammonia plant


CA-PE-5 Isothermal CO converter for ammonia production

CA-OM-1 Humidification process prior to primary reformingin ammonia production process


CA-PE-6 CO oxidizer in ammonia production processCA-ME-3 High pressure water power recovery turbine in

ammonia production processCA-OM-3 Ammonia production process: Carbonate removal

process


CS-OM-2 Reduction of electrolytic power for NaClelectrolysis bath in caustic soda production process


CS-PE-3 Ion exchange membrane NaCl electrolysis bath forcaustic soda production

CA-ME-4 Installation of pre-reformer in ammonia reformingprocess

CA-ME-1 Waste heat recovery unit for synthesis gascompressor exit gas in ammonia productionprocess

CA-ME-2 Membrane separation hydrogen recovery unit inammonia production process

CS-ME-2 Improvement of active cathode for ion exchangemembrane electrolysis for caustic soda production

138 -139

Chemical (Caustic soda) : Production Process and Energy Saving Technology

Caustic soda production process


CS-PE-3 Ion exchange membrane NaCl electrolysis bath forcaustic soda production

CS-PE-2 Energy saving ion exchange membrane electrolysisbath for caustic soda production

CS-ME-1 Brine preheater using recovered heat of NaClelectrolysis in caustic soda production process

CS-ME-2 Improvement of active cathode for ion exchangemembrane electrolysis for caustic soda production

CS-OM-1 Caustic soda production process: Switching fromdiaphragm electrolytic process to ion exchangemembrane electrolytic process

CS-OM-2 Reduction of electrolytic power for NaCl electrolysisbath in caustic soda production process


CS-PE-1 Quadruple-effect concentration for diaphragm-typeelectrolytic caustic soda production

140 -141

Chemical (Naptha Cracking) : Production Process and Energy Saving Technology

Naptha cracking production process


CN-ME-1 Switching quenching tower trays to packing in naphtha cracking processCN-ME-2 Installation of turbo-expander in top gas line of demethanizing column

in naphtha cracking processCN-ME-3 Cold heat recovery from demethanizing column bottom liquid in naphtha

cracking processCN-ME-4 Combustion air preheating for boilers using cooling tower bottom hot

water in naphtha cracking processCN-ME-5 Hot water heating by distillation column top vapor

CN-OM-1 Control of excess air ratio at cracking furnace in naphtha crackingprocess

CN-OM-2 Change of feed step for depropanizing column in naphtha crackingprocess

CN-OM-3 Pressure control of ethylene rectification column by suction pressure ofpropylene refrigerator in naphtha cracking process

CN-OM-4 Naphtha cracking process: Energy saving in ethylene cracker

142 - 143

Chemical(BTX) : Production Process and Energy Saving Technology


CB-ME-1 Recovery of top vapor heat of ortho-xylene separationcolumn in aromatics production process

CB-ME-2 Waste heat recovery from heating furnace flue gas inBTX production

CB-ME-3 Steam turbine power generation using waste heat ofdistillation column top vapor in BTX productionprocess

CB-OM-1 Change of washing system in amine desulfurizationprocess for BTX production

CB-OM-2 Reboiler heating by waste heat of top vapor ofdistillation column in BTX production process

CB-OM-4 Control of reflux ratio of distillation column usingon-line analyzer

144 -145

Data Sheets

3-1 Ammonia

3-2 Caustic Soda

3-3 Naphtha Cracking

3-4 BTX

3-5 General

146

[Energy Source]

[Practical Use]

[Industry Classification]

[Technology Classification]

Energy Conservation Directory

147

Fuel (general) Steam

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks

[Example sites] [References] [Inquiry]

After 1960

CA-PE-1

An evaporator used for vaporizing aqueous solution containing nonvolatile substances in a chemical plant.

1. For a multi-effect evaporator with n-stage, the consumption of heating steam is theoretically 1/n times.2. If the number of stages is increased at aspecific temperature difference, the temperature difference per stage

becomes small, thus the heat transfer area increases.3. Accordingly, the number of stages less than 6 is generally adopted, taking into account of the investment and

operating cost.4. Figure shows a multi-effect (2-stage) distillation flow scheme.

Chemical : Ammonia

Energy Conversion Forum, "Energy UtilizationEngineering," P190, Ohm Sha, 1980.

Production Equipment

1. The saturation temperature of generated vapor is lower than the boiling point of the solution, correspondingto the boiling point rise.

2. In the next evaporator in which the pressure is further reduced, the boiling point of the solution is lowerthan the saturation temperature of the vapor generated in the preceding stage.

3. The vapor generated in the preceding stage is used as the heat source of the next evaporator with reducedpressure. Vaporizers in which pressure is reduced from the preceding stage are installed in a train to use thevapor generated in preceding stage.

This type of facility is called a multi-effect evaporator.

The steam consumption becomes 0.7 to 0.8 times the steam consumption of a single stage evaporator dividedby the number of stages. That is, the general formula given below determines the steam consumption.

Multi-effect evaporator

Q = Qs/knwhere, Q : steam consumption for a n-stage evaporator

Qs : steam consumption for a single stage evaporator n : number of stages k : effectivity factor (normally 0.7 to 0.8)

Production of nonvolatile products such as NaCl and NaOH.Production of concentrated fruit juice.Concentration and solidification of nonvolatile matters in waste liquid.Desalination of sea water.

Japan Chemical Industry Association /ECCJ (JIEC)

Fig. 1 Liquid supplying method example of multi-effect evaporator

Improved section

Investment amount: 130 million yenImprovement effect: 40 million yen/yearInvestment payback: 3.2 years

[Energy Source]

[Practical Use]




148

Fuel (natural gas)

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1990s -

CA-PE-2

By using the reactor in the reforming process of an ammonia plant, the high-temperature process waste heat atthe exit of the secondary reformer is utilized as the reaction heat for the endothermic reaction in the primaryreforming process to achieve energy saving.

[Structure of heat-exchanger-type reactor] (Refer to Fig. 1)1) The primary reformer is used as a heat-exchanger-type reactor.

The heat transfer tubes are filled with Ni-based catalyst, and theexit gas of the secondary reformer flows through the shell side asheating fluid.

2) The catalyst tubes are of a double-tube type, where inner tubesare inserted into outer tubes. The mixture of preheated feed natu-ral gas and steam flows through an annular space filled with cata-lyst between the outer tube and the inner tube.

3) The mixture flows downward through the catalyst bed while be-ing reacted, then turns upward inside of the inner tube to enterthe secondary reformer.

4) Each outer tube is surrounded by a sheath tube, and the hot gasfrom the secondary reformer flows through the annular spacebetween these tubes.

Chemical : Ammonia

Makers’ in-house technical documents“Chemical Process” p. 50, 51, Tokyo KagakuDojin


1) Process waste heat of about 1,000˚C at the exit of the secondary reformer is utilized as the reaction heat(endothermic reaction) in the primary reformer.

2) The principle is to use the primary reformer as a heat-exchanger-type reactor. The heat transfer tubes arefilled with Ni-based catalyst. The exit gas of the secondary reformer flows through the shell side, and worksas heating fluid.

Table 1 Energy saving effect by heat-exchanger-type primary reformer (production capacity: 2,000 t/D)

Fig. 2 Improved reforming process flow of ammonia plant

Adopted at many sites.

Heat exchanger type primary reformer for

waste heat recovery in ammonia production process

[Improved process flow] (Refer to Fig. 2)

Fig. 1. Heat-exchanger-type primary reformer


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tnelaviuqelioedurcninoitcudeR y/Lk807,01

Improved section

Investment amount: 200 million yenImprovement effect: 200 million yen/yearInvestment payback: 1 year

[Energy Source]

[Practical Use]




149

Fuel (natural gas)

Outline

Principle

&

Mechanism

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1970s ~

CA-PE-3

The facility is an energy saving type reactor which is placed between the reactors of synthesis process ofammonia plant and which effectively recovers the heat of exit gas while controlling the reaction heat to main-tain the reaction temperature at an adequate level through the heat exchange with the reactor inlet gas.

[Features of the high conversion synthesis reactor (indirect cooling reactor)]1) The method uses the inlet gas of the reactor to cool the hot exit gas at each catalyst bed through a heat

exchanger. Thus, the disadvantages of cool gas quenching method are solved.2) The indirect cooling reactor gives the exit gas temperatures of the reactor from about 300˚C to 450 - 500˚C,

which temperature allows effective use of the reaction heat to generate high pressure steam and superheatedsteam. The method achieves energy saving of about 0.14 x 106 kcal/t-NH

3 of unit requirement compared

with that of conventional quenching method.3) Fig. 1 shows an example of indirect cooling high conversion synthesis reactor.

Chemical : Ammonia


1) There are two methods for removing reaction heat in the ammonia synthesis reactor: the indirect coolingmethod that employs a heat exchanger having the structure that is applied in this case; and the quenchingmethod which uses unreacted synthesis gas directly for cooling.

2) Conventionally-applied quenching method has a simple structure facility. The method has, however, disad-vantages that the ammonia concentration which was increased by the synthesis reaction is diluted by thecooling gas and that the temperature at exit of the reactor is lowered.

3) Owing to the drawbacks, recent ammonia synthesis plants have adopted a new synthesis reactor of indirectcooling method.

Table 1 Improvement in unit requirement of high conversion synthesis reactor (production rate of 300,000 t/y)

Fig. 1 Schematic drawing of cross section of indirect cooling high conversion synthesis reactor

Ammonia plant

High conversion synthesis reactor

[Description]

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)sisablioedurc(ygrenefonoitcudeR y/Lk807,5

Improved section

Adopted at some sites. Makers’ in-house technical documentsJapan Chemical Industry Association / ECCJ (JIEC)


[Energy Source]

[Practical Use]




150

Fuel (natural gas)

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CA-PE-4

The improvement is related to an energy saving reactor of ammonia synthesis process, in which the direction ofgas flow within the reactor catalyst bed is controlled to reduce the pressure loss.

[Features of low pressure difference reactor]1) Conventional synthesis reactor employs

axial gas flow direction through the cata-lyst bed, which induces pressure differ-ences of from 7 to 14 kg/cm2. The newdesign of reactor which uses the gas flowdirections of radial, cross sectional, andaxial-radial significantly reduces the pres-sure difference. Reduction of pressure dif-ference reduces the power consumption ofthe circulator. (Refer to Table 1.)

2) The developed low pressure difference re-actor allows to reduce the catalyst particlesize from 6 - 12 mm to 1.5 - 3 (6) mm,thus the catalyst activity is improved theconversion at exit of reactor is improved,and the exit ammonia concentration is in-creased.

3) Increased conversion reduces the circula-tion gas rate, thus decreases the power con-sumption of the circulator.

4) Increased ammonia concentration at exitof the synthesis reactor increases the con-densation temperature, increases the con-densed generated ammonia by water cool-ing, thus decreases the condensed refrig-erant ammonia and decreases the powerconsumption of the refrigerator.

Chemical : Ammonia

Makers’ in-house technical documents


A feature of the ammonia synthesis process is unavoidably forming a synthesis loop. The pressure difference inthe synthesis loop reaches to a range of from 7 to 14 kg/cm2. With the use of a low pressure difference typesynthesis reactor, energy saving resulted from reduced pressure difference and packing of small sized syntheticcatalyst particles owing to the reduction of pressure difference are available. Since the catalyst of small particlesize has high activity, the conversion increases and the driving energy for circulator and refrigerator decreases.

Table 2 Reduction in unit requirement in a pressure difference reactor

Fig. 1 Schematic cross sectional drawing of radial direction flow reactor

Adopted at some sites.

Table 1 Comparison of gas flow directions and

of power consumption

Ammonia plant

Low pressure difference synthesis reactor

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tnemevorpmifotceffE

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wolfnoitceridlanoitcesssorC HN-t/hWk933

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wolfnoitceridlaidaR HN-t/hWk733

HN-t/hWk73

wolfnoitceridlaidar-laixA HN-t/hWk233

HN-t/hWk213

Improved section

Japan Chemical Industry Association / ECCJ (JIEC)

Investment amount: million yenImprovement effect: million yen/yearInvestment payback: years

[Energy Source]

[Practical Use]




151

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1990s ~

CA-PE-5

The converter is a reactor with built-in heat exchanger to implement the CO conversion in the ammonia plant ata single stage and to recover the reaction heat.

1) Conventionally, an adiabatic reactor filled with Fe-Cr catalyst (usually) is operated to conduct two stagereactions: namely, the high temperature conversion operated at temperatures of from 370 to 430˚C, and thelow temperature conversion operated at temperatures of from 200 to 230˚C.

2) The facility adopts an isothermal reactor to carry out the reaction in a single stage at about 250˚C.The reaction heat generated by the CO conversion in the reactor is recovered by generating medium pres-sure steam in a built-in heat exchanger.

3) Fig. 1 shows the reactor used in the CO conversion process in the ammonia plant.

Chemical : Ammonia


1) The secondary reformer exit gas contains about 13 vol.% of CO.The CO is converted to H

2 by the reaction of

CO + H2O = CO

2 + H

2The reaction is advantageous in terms of chemical equilibrium at lower temperatures.

Table 1 Effect of improvement of energy unit requirement during ammonia production

(at operation rate of 100,000 t/y)

Fig. 1 Reactor used in the CO conversion process

Ammonia plant

Isothermal CO converter

The facility is also applicable to hydrogen plants.

“Energy Saving Journal (Vol. 31, No. 8, 1979),”

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tnemevorpmiehtfotceffE

maetssaderevocertaeH 01x1.0 6 HN-t/lack3


Improved section


Investment amount: 500 million yenImprovement effect: 2,560 million yen/yearInvestment payback: 0.2 years

[Energy Source]

[Practical Use]




152

Fuel (natural gas)

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1971~

CA-PE-6

The improvement relates to the CO conversion step in ammonia plant, particularly to the unit which conductstwo stage reactions at high and low temperature levels, (CO + H

2O = CO

2 + H

2), followed by oxidizing the

residual CO with air on a Pd catalyst to obtain CO2.

1) The CO remained after the conversion is converted to CH4 in the downstream methanation stage. The CO

is, however, accumulated in the synthesis reaction to hinder the reaction.2) The unit oxidizes CO into CO

2 using a catalytic reaction, which CO

2 is removed in succeeding carbonate

removing stage. Increased purity of syn-gas decreases the amount of purge gas in the synthesis stage. As aresult, the H

2 loss also decreases.

3) Fig. 1 shows the ammonia production flow diagram with the addition of the CO oxidizer.

Chemical : Ammonia


[Pd metal catalyst]The catalyst selectively oxidizes CO remained at 0.3 to 0.5 vol.% after the CO conversion, into CO

2 gas. Since

the treatment reduces CO amount, the amount of CH4 generated in downstream methanation stage decreases,

which improves the purity of the syn-gas.

Table 1 Improvement in energy unit requirement in CO converter (at production rate of 300,000 t/y)

Fig. 1 Flow diagram of CO conversion in ammonia production process

CO oxidizer in ammonia production process

The facility is also applicable to hydrogen plants.

Makers’ in-house technical documents Japan Chemical Industry Association / ECCJ (JIEC)Adopted at some sites.

Improved section

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ygrenederevoceR 01x70.0 6 HN-t/lack3

ygrenefonoitcudeR y/Lk158,2


[Energy Source]

[Practical Use]




153

Outline

Before

Improvemet

[Description

&

Improvement]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1984

CA-ME-1

In an ammonia plant, in-process heat recovery from compressed gas out of the synthesis-gas compressor wasnot applied because the heat exchanger hinders temperature control in the succeeding process. For effective useof the heat exchanger, the boiler feed water is injected into the process gas, thus the temperature control be-comes possible. Feed steam to the reboiler of the CO

2 regenerator is decreased as well owing to the increase in

the heating value.

1) When the heat is exchanged with the compressor exit gas, the inlet temperature of the low-temperatureconverter increases from 214˚C to 238˚C. The boiler feed water at 130˚C is injected into the process gas tochange the sensible heat to the latent heat. In this manner, the heating value increases without raising thetemperature, which is maintained at the set level of 214˚C. (Refer to Fig. 2)

2) This improvement increases the supply rate of latent heat to the process reboiler of the CO2 regenerator.

Accordingly, the load of feed steam to the steam reboiler can be decreased.

Chemical : Ammonia

Machinery & Equipment

Feed gas generated in the reformerwas purified, compressed by the am-monia synthesis-gas compressor from24 kg/cm2 to 150 kg/cm2 , and fed.A heat exchanger to preheat themethanator feed gas was installed asthe intercooler of this compressor.The heat exchanger was, however, notused because it gives bad influenceto the control of the inlet temperatureof the low-temperature converter ofthe succeeding process. It also short-ens the catalyst life. Thus the heat ofcompression was discarded into cool-ing water. (Refer to Fig. 1)

Table 1 Energy saving effect

Fig. 2 System to inject boiler feed water to low-temperature converter

Mitsui Toatsu Chemicals’Osaka plant

“Collection of Energy Conservation Cases1985,” p. 1223

FuelWaste heat recovery unit for synthesis gas

compressor exit gas in ammonia production process

Fig. 1 Flow chart of synthesis gas purification and compression process

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reliobermaetsotylppusmaetsninoitcudeR h/t275.3


Improved section

Improved section


Investment amount: 60 million yenImprovement effect: 30 million yen/yearInvestment payback: 2 years

[Energy Source]

[Practical Use]




154

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1979 ~

CA-ME-2

The membrane separation unit is an energy saving unit which does not employ any moving parts and does notneed any complex operation while consuming minimum energy, because the separation is carried out using thepressure of the gas itself as the driving force.

[Structure of hydrogen separation membrane]1) The gas separation membrane used for hydrogen gas recovery is made of a non-porous polymer which has

excellent properties in the heat resistance, pressure durability, chemicals resistance, separation coefficientand permeation rate.

2) The membrane element is either a hollow type having approximate diameters of 0.1-0.5 mm or a flat mem-brane wound in a spiral form. These elements are packed in a pressure vessel to form a module. (Refer toFig. 1.)

Chemical : Ammonia


[Features of the membrane separation process]1) The process attains high hydrogen recovery rate in a high-pressure process, and is suitable for a process for

producing hydrogen of the concentration of 90-99%.2) After installed, the throughput can be readily changed responding to the operating conditions.3) The process has no moving part, and saves energy. Its maintenance is easy.4) The product hydrogen has a low pressure owing to the permeation treatment.5) Condensation of the heavy fraction in feed gas results in the decrease in the hydrogen permeation rate. To

prevent it, an adequate pre-treatment is required.6) The investment cost is low.

Table 1 Improvement effect in specific consumption by membrane separation hydrogen recovery

(production rate of 300,000 t/y)

Fig. 1 Schematic cross section of separation membrane module

Adopted at some sites.“Oil Refinery Process (Japan Petroleum Society)”Kodansha

Fuel (natural gas)

- Energy saving effect

Membrane separation hydrogen recovery unit

in ammonia production process

Principle

&

Mechanism

[Description]

- Additional effect: From the same volume of natural gas, the production is increased by 4-6% comparedwith conventional process.

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Improved section


[Energy Source]

[Practical Use]




155

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CA-ME-3

This improvement is to utilize a high-pressure water turbine in order to recover power from the high-pressureliquid which absorbed carbon-dioxide in the carbon-dioxide removal process of an ammonia plant.

[Before the improvement]1) In the carbon-dioxide removal process, a large quantity of absorbent liquid is supplied to the top of the

absorbing column under a pressure of about 30 kg/cm2 to remove about 15 vol.% of CO2 contained in the

crude gas coming from the reforming process and the CO conversion process.2) The liquid which absorbed CO

2 is sent to the regenerating column after the pressure is reduced from 30 to 1

kg/cm2 by a pressure-reducing valve.

[After the improvement]1) The facility employs a power recovery turbine instead of the pressure-reducing valve, and utilizes the pres-

sure to drive the feed pump for the absorbent liquid.2) The facility comprises an electric motor with shafts on both sides, which are directly connected to a power

recovery turbine and to a absorbing liquid feed pump via clutches.

Chemical : Ammonia


[Power recovery system using high-pressure water turbine and power recovery calculation formula]

Table 1 Energy saving effect by power recovery turbine

Fig. 1 Flow diagram of waste heat recovery of primary reformer of ammonia plant

Adopted at many sites. “Hydrocarbon Processing (Aug.1992)

Fuel (natural gas)High pressure water power recovery turbine in

ammonia production process

Principle

&

Mechanism

[Description]

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Improved section



[Energy Source]

[Practical Use]




156

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CA-ME-4

This technology is a process improvement aiming at energy saving by installing a pre-reformer in the reformingstage of the ammonia production process.

1) Using high-temperature (600˚C or more) waste heat of the primary reformer flue gas, the mixture of feednatural gas and reaction steam is heated up to 620˚C.

2) The heated mixture is sent to the primary reformer, where the feed natural gas is cracked by steam on a Nicatalyst to yield H

2, CO, and CO

2.

3) Part of the primary reforming reaction is carried out in the pre-reformer (adiabatic reformer) which is alsofilled with a Ni catalyst. Since the reaction heat (endothermic reaction) is supplemented by the sensible heatof the mixture, the exit gas temperature is lowered by 60-80˚C.

4) The reactor exit gas is reheated by the flue gas, which is then fed to the primary reformer.5) Installation of the pre-reformer allows to reduce the capacity of the primary reformer by 10%.

Chemical : Ammonia


- The conventional process adopted natural gas reforming by the primary reformer.

Table 1 Energy saving effect by pre-reformer

Fig. 1 Flow chart of reforming process with pre-reformer

(Note *: Production capacity of 2,000 t/d, operating days of 330 d/y)

“Hydrocarbon Processing (Aug. 1992)”

Fuel (natural gas)Installation of pre-reformer in

ammonia reforming process

Before

Improvemet

[Description

&

Improvement]


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Improved section



[Energy Source]

[Practical Use]




157

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CA-ME-5

This unit preheats the combustion air by hot flue gas generated by combustion, and supplies the heat to theendothermic reaction (reforming reaction) in the heating-furnace-type primary reformer of an ammonia plant.

Chemical : Ammonia


1) In the primary reformer, fuel is combusted outside of catalyst tubes to supply heat to the reforming reaction(endothermic reaction) in the catalyst tubes. The waste heat of the flue gas (about 1,000˚C) generated bycombustion is used to heat the feed natural gas, process air, and steam.

2) To increase the thermal efficiency of the primary reformer, the waste heat of the flue gas needs to be utilizedto a temperature as low as possible by using it to heat low-temperature fluids.Combustion air for the primary reformer is one of the low-temperature fluids. Waste heat is used to heat thecombustion air from the normal temperature to temperatures of 200 to 400˚C, thus the fuel consumption ofthe primary reformer is reduced.

Table 1 Energy saving effect by waste-heat recovery

Fig. 1 Flow chart of ammonia plant primary reformer waste heat recovery


(Remark*: Ammonia production 2,000t/D, operation days 330 days/year)

NEDO reports

Fuel (natural gas)Primary reformer waste heat

recovery unit for ammonia plant

Principle

&

Mechanism

[Description]

This technology was demonstrated at Sichuan Chemical Complex in Sichuan province of China as the NEDO’sModel Project for Ammonia Primary Reformer Waste Heat Recovery.

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]BesaC[004foerutarepmetgnitaeherP

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Improved section


[Energy Source]

[Practical Use]




158

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CA-OM-1

The case is a process improvement to humidify the feed natural gas with the process condensate, as a part of thehumidifying steam, by spraying into the natural gas and by vaporizing the process condensate using the heat ofpreheated natural gas, before entering the primary reformer of the ammonia plant.

Chemical : Ammonia

Operation & Management

(1)For primary reforming natural gas, the natural gas is preheated to 400˚C before subjected to desulfurization.The process steam (40 kg/cm2G) is added to thus desulfurized natural gas to a level of S/C molar ratios offrom 3.0 to 3.5. Then the natural gas is again preheated to 620˚C, and is fed to the catalyst tubes to performreforming.

Table 1 Effect of energy saving by the humidification process

Fig. 1 Humidification flow diagram of before the primary reforming


FuelAmmonia production process

Pre-humidification process for primary reforming

Before

Improvement

[Description

of

Improvement]

The technology is applicable also to methanol plants and hydrogen plants.

(1)The low temperature waste heat at about 200˚C ofthe flue gas of the primary reformer is utilized.

(2)The process natural gas is preheated to about 200˚Cby the flue gas, and is desulfurized, followed byfeeding to the bottom of the saturation tower.On the other hand, the process condensate issprayed form the top of the saturation tower tomake contact with the warmed natural gas to satu-rate with water. The saturated natural gas is usedas a part of the 42 bar reforming steam.

(3)After adding the steam to the natural gas to satisfythe necessary total amount of steam, the naturalgas is again preheated, and is fed to the catalysttubes of the primary reformer to perform the re-forming.

Some sites adopting similar technology

tceffE krameR

tnemeriuqertinuygreneninoitcudeR 01x50.0 6 HN-t/lack3

foetarnoitcudorPy/t000,001

tnemeriuqertinurewopniesaercnI HN-t/hWk13


Improved section



[Energy Source]

[Practical Use]




159

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1986

CA-OM-2

Melamine which is synthesized from urea is dissolved into aqueous ammonia in the pressurized quencher,followed by depressurized and cooled in the crystallizer to yield crystalline melamine. The improvement isenergy saving through preheating the filtrate discharged from centrifugal separator in the crystallizing step forammonia recovery.

Chemical : Ammonia


Fig. 1 Process flowchart of ammonia recovery from filtrate after separating melamine

Table 1 Improved effect of energy saving in the ammonia recovery step

Fig. 2 Flowchart of ammonia recovery

(before improvement)


“Collection of Energy Conservation Cases 1980,”p.1021

Fuel (steam)Ammonia production process

Improvement in heating feed to ammonia stripper

Description

of

Process

[Description

of

Improvement]

The improvement is a typical example of widely utilizing methods for preheating raw material feed for all kindsof distillation columns.

[Before improvement]


[After improvement]

The temperature of residue as the heating mediumwas 51˚C at the exit of filtrate preheater.

Before the existed preheater in the filtrate feed line tothe distillation column, an additional preheater is in-serted in series, thus the temperature of filtrate is in-creased.

Fig. 3 Flowchart of ammonia recovery

(after improvement)

tceffedevorpmI krameR

noitpmusnocmaetsfonoitcudeR h/t0.31 )y/h000,4:emitgnitarepO(


Improved section

Investment amount: 7 million yenImprovement effect: 3.3 million yen/yearInvestment payback: 2.1 years

[Energy Source]

[Practical Use]




160

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CA-OM-3

The improvement is the one for energy saving in the carbonate removal process of ammonia production pro-cess.

Chemical : Ammonia


[Before improvement](1)Conventional carbonate removal applies chemical absorption method using an absorbing liquid such as

monoethanolamine (MEA) aqueous solution. The method removes CO2 contained at about 18 vol.% in the

crude synthesis gas coming from the CO conversion process.(2)The regeneration heat of the solution after absorbing CO

2 is about 1,000 to 2,000 kcal/Nm3-CO

2.

(3)With natural gas as the raw material, the quantity of removed carbonate is about 620 Nm3-CO2/t-NH

3, and the

process is the largest consumer of energy in the ammonia plant.

Table 1 Improved effect in the carbonate removal process in the ammonia production process

(production capacity: 300,000 t/y)

Fig. 1 Flowchart of energy saving type carbonate removal process



Fuel (natural gas)Ammonia production process

Carbonate removal process

Before

Improvement

[Description

of

Improvement]

[After improvement](1)The improved technology for removing carbonate is the physical absorption type (Selexol process). The

regeneration of the solution is performed by vacuum flashing and air stripping. As a result, the energyrequired for regeneration of the solution is significantly reduced to 22 kcal/Nm3-CO

2.


retfatnemeriuqertinudecudeRtnemevorpmi

tceffetnemevorpmI


noitpmusnocrewopdesaercnI HN-t/hWk013


Improved section

Investment amount: 1,200 million yenImprovement effect: 470 million yen/yearInvestment payback: 2.5 years

[Energy Source]

[Practical Use]




161

Fuel (steam)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1977

CS-PE-1

When the electrolytic production method of industrial salt is converted from the mercury process to the dia-phragm process, the electrolyte generated in the process becomes a dilute NaOH solution containing a largeamount of NaCl salt. Accordingly, it is necessary to concentrate the NaOH by a concentrator to about 50% toseparate the salt in a form of crystals. This improvement enhances energy efficiency and saves energy bymodifying the existing triple-effect concentration method to the quadruple-effect concentration method.

1) The electrolyte generated in thediaphragm process is a dilutesolution of NaOH (about 10%).It also contains NaCl of about15%. It is necessary to concen-trate the NaOH by a concentra-tor to about 50% to separate thesalt as crystals.

2) The existing triple-effect concen-tration method is modified to thequadruple-effect concentrationmethod. The energy efficiencyis improved, and the steam con-sumption is reduced by 26%.The flow chart of the quadruple-effect evaporation vessels isshown in Fig. 1.

3) Comparison of triple-effectevaporation and quadruple-effectevaporation. (Refer to Table 1)

Chemical : Caustic Soda

Many sites adopting similartechnology

“Energy Saving Journal (Vol. 30, No. 9,1978),” P. 45


Fig. 1 Flow chart of caustic soda concentration by quadruple-effect evaporation vessels

Table 1 Comparison of triple-effect evaporation and

quadruple-effect evaporation

Table 2 Energy saving effect by quadruple-effect evaporation

Quadruple-effect concentration for diaphragm-type

electrolytic caustic soda production

Note*: Operating hours: 7,000 h/y

epyttceffe-elpirT epyttceffeelpurdauQ tceffetnemevorpmI

noitpmusnocmaetscificepS HOaN-t/t7.2 HOaN-t/t0.2 y/t7.0ybnoitcudeR

*noitpmusnocmaetsninoitcudeR y/t000,007


noitaropavetceffe-elpurdauQ noitaropavetceffe-elpirTerutarepmeT noitartnecnoC erutarepmeT noitartnecnoC

rotaropave1.oN C˚851 %34 C˚241 %54rotaropave2.oN C˚201 %52 C˚78 %52rotaropave3.oN C˚67 %71 C˚35 %61rotaropave4.oN C˚05 %21 - -

Concentration of electrolyte NaOH 10.3wt% NaCL 15.1wt%Concentration of product NaOH 50 wt% NaCL 1.1wt%

Improved section

Japan Chemica Industry Association /ECCJ(JIEC)

Investment amount: 4,560 million yenImprovement effect: 1,140 million yen/yearInvestment payback: 4 years

[Energy Source]

[Practical Use]




162

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1994

CS-PE-2

The newly developed electrolysis bath gives less voltage drop owing to its structure compared with a conven-tional multi-polar ion-exchange-membrane electrolysis bath. Accordingly it allows to increase the currentdensity, making it an energy-saving compact NaCl electrolysis bath. Compared with a conventional type, itachieves power saving of about 6%.

The current flows as indicated in Fig.1. As the electric conductivity of Ni issix times that of Ti, a minimum levelof current flows through the Ti section.Owing to this structure, the voltagedrop becomes less.


Adopted at some sites. Japan Chemical Industry Association /ECCJ (JIEC)

“Soda Industry Technical Information (No. 449),”Oct. 1994


Fig. 2 Configuration of multi-polar element

Fig. 1 Cross section of multi-polar element

Fig. 3 Flow of electrolyte

Table 1 Power saving effect of improved type compared with conventional multi-polar

ion-exchange-membrane electrolysis bath

Energy saving ion exchange membrane

electrolysis bath for caustic soda production

The technology is economically applicable to the operation with a high current density up to 6 kA/m2.

noitpmusnocrewopcificepsninoitcudeR HOaN-t/hWkCD131 :noitidnocgnitarepO,y/HOaN-t000,001fonoitcudorp

2m/Ak3ytisnedtnerructnelaviuqelioedurcninoitcudeR y/Lk381,3

Improved section

Improved section


[Energy Source]

[Practical Use]




163

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1992

CS-PE-3

This technology is to switch the method employed in the NaCl electrolysis bath for caustic soda productionfrom the asbestos membrane method to the bag ion exchange method. This improvement significantly reducedelectric power consumption.

[Features of ID-process NaCl electrolysis bath](Refer to Fig. 1)

1) Caustic soda and chlorine generated by elec-trolysis of saline water are separated by an ionexchange membrane.

2) The ion exchange membrane is formed to a bagby which the saline water and pure water aresealed from each other more easily than a flatmembrane.



Fig. 2 Modification of cathodic can

Fig. 1 Schematic drawing of electrolysis bath

Fig. 3 Comparison of anode before and after improvement

Table 1 Comparison of energy saving effect between conventional membrane method

and ion exchange membrane method for electrolysis bath

Ion exchange membrane NaCl electrolysis bath for

caustic soda production

[Improvement of ID-process NaCl electrolysis bath] (refer to Figs. 2 and 3)1) The electrolysis bath was switched from the asbestos membrane method to the bag-shaped ion exchange

membrane method.2) The cathodic material of the cathodic can was switched to SUS310S. The mounting method was also modi-

fied.3) The inner material of the can nozzle was changed to SUS310S.4) The treatment of the periphery of the anode was modified. The thickness of the Ti spring was increased and

the flatness was improved.

enarbmemlanoitnevnoCdohtem

egnahcxenoidevorpmIdohtemenarbmem

tceffE

tixehtabsisylortceletanoitartnecnocHOaN %21 %43

tixehtabsisylortceletanoitartnecnoctlaS %41 %300.0

noitpmusnocrewopcificepS HOaN-t/hWk595,2 HOaN-t/hWk833,2 HOaN-t/hWk752

noitpmusnocmaetscificepS HOaN-t/t4.2 HOaN-t/t24.0 HOaN-t/t89.1


“Soda Industry Technical Information (No. 449),”Oct. 1994

Improved section

Improved section

Adopted at some sites. Japan Chemical Industry Association /ECCJ (JIEC)

Investment amount: 2,015 million yenImprovement effect: 447.8 million yen/yearInvestment payback: 4.5 years

[Energy Source]

[Practical Use]




164

Fuel (steam)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1992

CS-ME-1

This improvement is to install a preheater which preheats brine (NaCl water) fed to the electrolysis bath, usingsensible heat of chlorine and hydrogen gases generated in the membrane electrolysis bath.


Adopted at some sites. “Soda Industry Technical Information (No. 449),”Oct. 1994


Table 1 Materials of main parts of brine preheater

Fig. 1 Flow diagram of brine preheating syste

Table 2 Heat recovery effect of brine preheater

[Before improvement]Conventionally, the feed brine was heated by steam using a carbide-made heat exchanger.

[After improvement]1) After the improvement, the heat is exchanged with the sensible heat of chlorine and hydrogen gases gener-

ated in the NaCl electrolytic bath (particularly membrane-type electrolysis bath), thus the steam consump-tion is reduced compared with the conventional steam heating.

2) Fig. 1 shows the flow diagram around the preheater.3) The heat exchanger is a shell-and-tube type. The materials of the main parts are listed in Table 1.

Brine preheater using recovered heat of NaCl

electrolysis in caustic soda production process

edisllehS edisebuT

enirb-sagenirolhC )muinatiT(53PT )muinatiT(W53HTT

enirb-sagnegordyH )SS(V04SS )SS(W53HTT

tceffE krameR

)tnelaviuqemaetsni(yrevocerygrenE y/t000,81 005,71(y/enirolhc-t000,55:etarnoitcudorP)negordyhfo3mktnelaviuqelioedurcninoitcudeR y/Lk864,1


Improved section


[Energy Source]

[Practical Use]




165

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1985

CS-ME-2

This improvement is to use an active cathode. This type of cathode was developed to reduce the overvoltage atthe cathode which generates large energy loss in ion-exchange-membrane NaCl electrolysis for caustic sodaproduction. Focusing on the fact that the overvoltage at an electrode depends on the electrolysis voltage and itssurface area, a new coating method was adopted, which significantly widens the surface area of the electrode.Thus, the power consumption was remarkably reduced.

[Principle of ion-exchange-membrane method and breakdown of energy loss]


Some sites adopting similar tech-nology

Japan Chemical Industy Asociation /ECCJ (JIEC)

“Collection of Energy Conservation Cases 1988,”p. 197


Fig. 1 Mesh-type cathode

Fig. 1 Schematic drawing of electrolysis bath

Fig. 2 Schematic drawing of the cross section of cathode

Table 1 Example of energy saving (Production scale of 100,000 t-NaOH)

[Structure of active cathode]1) Fig. 2 shows the mesh-type cathode. Fig. 3 illustrates its cross section. Special coating is applied on the

stainless or nickel cathode, and the hydrogen overvoltage is reduced.2) The coating layer is a Ni-C-S porous alloy.3) For normal industrial-scale production, the operating current density is 20-40 a/dm3. The overvoltage of the

active cathode is reduced by more than 0.2 V compared with that of a conventional one.

Improvement of active cathode for ion exchange

membrane electrolysis for caustic soda production

noitpmusnocrewopcificepsninoitcudeR )HOaN-t(/hWk051

noitcuderrewoplaunnA y/hWk000,000,51


rewopcificepsninoitcudeR)HOaNt/hWk(noitpmusnoc

)%(etaR

ecnatsiserenarbmem-egnahcxe-noI 543 3.04

ecnatsiserdiuqiledonA 51 8.1

ecnatsiserdiuqiledohtaC 35 1.6

egatlovrevoedonA 76 9.7

egatlovrevoedohtaC 362 7.03

ecnatsiserrotcudnoC 211 2.31

latoT 557 0.001

Table 1 Breakdown of energy loss in ion-exchange-membrane electrolysis

Improved section

Improved section

Investment amount: 255.1 million yenImprovement effect: 72.9 million yen/yearInvestment payback: 3.5 years

[Energy Source]

[Practical Use]




166

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1988

CS-OM-1

In the past, caustic soda production was conducted by the diaphragm process in which anode and cathode in theNaCl electrolytic bath were separated by an asbestos diaphragm from each other. There developed a process toproduce high concentration and high purity caustic soda through electrolysis using ion exchange membrane.The ion exchange membrane process gives significant energy saving compared with conventional diaphragmprocess.

[Principle of diaphragm process electrolytic bath and of ion exchange process electrolytic bath]





Fig. 3 Flowchart of diaphragm process

Fig. 1 Conceptual drawing of diaphragm

process electrolytic bath

Table 2 Energy saving effect through the switching to ion exchange membrane process

(basis: 100,000 t/y of production)

[Conventional process] Refer to Fig. 3(1)Caustic soda yielded in the electrolytic bath

needs further concentration and purification.NaOH concentration : about 12%NaCl concentration : about 16%

(2)Content of impuritiesNaCl : 0.86 ~ 0.93 %Na

2CO

3 : 0.082 ~ 0.180 %

Fe2O

3 : 0.0018 %

Fig. 2 Conceptual drawing of ion exchange process

electrolytic bath

Caustic soda production processSwitching from diaphragm electrolytic process to

ion exchange membrane electrolytic process

Fig. 4 Flowchart of ion exchange membrane process

New process] Refer to Fig. 4(3)Caustic soda yielded in the electrolytic bath

is the final product.NaOH concentration: about 20 to 35%

(4)Content of impuritiesNaCl : 0.0018 0.0072 %Na

2CO

3 : 0.018 ~ 0.09 %

Fe2O

3 : 0.00009 ~ 0.008 %

ssecorplanoitnevnoC ssecorpweN tnemevorpmifotceffE

tinurewopcirtcelEtnemeriuqer

sisylortcelerof HOaN-t/hWk005,2 HOaN-t/hWk001,2egareva noitcuder%61

rewoprof HOaN-t/hWk004-ot002 HOaN-t/hWk57egareva noitcuder%57

tnemeriuqertinumaetS HOaN-t/t2.3?2 HOaN-t/t86.0 noitcuder%47


“Chemical Engineering Journal (Vol. 56,No.9),” p.634

Improved section

Investment amount: 2,500 million yenImprovement effect: 616 million yen/yearInvestment payback: 4 years

[Energy Source]

[Practical Use]




167

The electrolytic power (W) of NaCl electrolysis is, as shown in equation (1), proportional to the bath voltage(V), which is in turn, as shown in equation (2), nearly in a linear relation with the current (I).The production rate (P) is proportional to the product of the current and the number of baths (n) as shown inequation (3).

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1977

CS-OM-2

In the past, caustic soda production was conducted by the diaphragm process in which anode and cathode in theNaCl electrolytic bath were separated by an asbestos diaphragm from each other. There developed a process toproduce high concentration and high purity caustic soda through electrolysis using ion exchange membrane.The ion exchange membrane process gives significant energy saving compared with conventional diaphragmprocess.


Similar technologies are adoptedat some sites.


where, W is the electrolytic power (==), 670 is the electrochemical equivalent (=), V is the bath voltage, hc isthe current efficiency, I is the load current (kA), a and b are the constants, P is the production rate, n is thenumber of baths, and K is a coefficient.

Table 1 Example of energy saving effect

1) Equation (3) suggests that, for a certain production rate, the load current can be reduced when the number ofbaths is increased. Equations (1) and (2) suggest that the power is saved by this approach. However, if thecurrent is simply reduced:

- The specific steam consumption for enriching increases due to the reduced concentration of electrolyte. - The current efficiency is reduced due to the increase in liquid resistance resulted from the decrease in the

electrolyte temperature. - The membrane is consumed and degraded due to the changes in the pH value in the membrane bath, and the

current efficiency is reduced.As the measures to these problems, - The reduction in the electrolyte concentration is prevented by adjusting the membrane and strictly control-

ling the electrolytic bath. - The electrolyte temperature is increased by about 2˚C by preheating the feed saline water using the waste

heat of generated hydrogen gas drain, thus maintaining the current efficiency.

Reduction of electrolytic power for NaCl electrolysis

bath in caustic soda production process


The improvement for a membrane NaCl electrolysis bath is illustrated. The technology is applicable to ion-exchange-membrane NaCl electrolysis bath and electrolytic production of high-purity chromium and manga-nese-dioxide.

tceffE krameR

noitpmusnocrewoplaunnaninoitcudeR y/hWk000,002,31 %4.7foetarnoitcudeR


(1)

(2)

(3)


Improved section


Energy Conservation Directory[Energy Source]

[Practical Use]



168

Electricity, Fuel

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1987

CN-ME-1

Fig. 2 Quenching column

(before improvement)

Table 2 Energy saving effect by changing trays to packing

Power consumption by the feed gas compressor of the naphtha cracking process is reduced by increasing thesuction pressure. The suction pressure is determined by the exit pressure of the cracking furnace and by thepressure difference across the quenching process. Since the increase in the exit pressure of the cracking furnacesignificantly reduces the ethylene yield, the pressure difference across the quenching process is reduced to saveenergy.

1) The pressure difference across the quenching processis 0.31 kg/cm2. The bottom oil of the quenching col-umn is recirculated to the gasoline-fractionating col-umn. The bottom oil-bearing hot water (quench wa-ter) of the quenching column is used as heat sourcesin various processes in the plant, and is recirculated toperform contact cooling after its temperature is con-trolled using cooling water.

2) In the both columns, the pressure difference occurs atthe valve tray sections. The pressure difference oc-curs at each tray according to the liquid depth. If thevalve trays are changed to packing, the pressure dif-ference is decreased and the heat transfer coefficientis increased, thus the top reflux is decreased and thebottom temperature is increased.

4) As a result, the heat source of the de-ethanizing column can be switched from low-pressure steam to quenchwater, so the steam consumption is reduced.

Chemical : Naphtha Cracking




[Process flow of the facility] (Refer to Fig. 1)The quenching process comprises a gasoline-fractionating column and a quenching column.

Fig. 1 Flow chart of naphtha-cracking quenching

process


Switching quenching tower trays to packing in

naphtha cracking process

Fig. 3 Tray packing section in quenching column(after improvement)

[After improvement]

Table 1 Comparison of operating conditions before and after improvement

noitcuderylruoH )y/h000,7(noitcuderlaunnA

noitpmusnocrewopninoitcudeR h/Wk076 y/hWk000,096,4

noitpmusnocmaetsninoitcudeR h/t9.5 y/t003,14


tnemevorpmierofeB tnemevorpmiretfA

nmulocgnitanoitcarf-enilosagniecnereffiderusserP-nmulocgnihcneuqssorcaecnereffiderusserP-

mc/gk70.0 2

mc/gk50.0 2

mc/gk10.0 2

mc/gk10.0 2

rosserpmocsagdeeffoerusserptelnI-.cte,rosserpmocsagdeeffoecrofgnivirD-

mc/gk94.0 2

h/Wk007,21mc/gk95.0 2

h/Wk030,21

retawhcneuqfoerutarepmeT C˚68 C˚88

maetsreliobeR h/t6.8 h/t7.2

Improved section




[Practical Use]



169

Electricity

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1991

CN-ME-2

Table 1 Energy saving effect by installing turbo-expander

This improvement is a measure to overcome capacity shortage of a refrigerant ethylene compressor underincreased ethylene production. In order to further reduce the pressure from the conventional level and lightenthe load to the compressor, a turbo-expander is installed in the top gas line and the low-temperature heat isrecovered for energy saving.

1) The top gas temperature of the demethanizing column, which was formerly changed under the isenthalpiccondition, is now lowered to -128˚C by using a turbo-expander, and further lowered to -136˚C by isentropicchange.

2) This improvement increases the heat recovery to 2.14 x 106 kcal/h, reduces the steam consumption at therefrigerant ethylene compressor by 4.5 t/h, and reduces the steam consumption at the refrigerant propylenecompressor by 3.2 t/h.

3) The process flow with the turbo-expander installed is shown below.

Adopted at some sites. “Collection of Energy Conservation Cases 1993,”p. 761


The conventional flow is given below.

Fig. 1 Flow chart around demethanizing column (before improvement)

Fig. 2 Flow chart around demethanizing column after turbo-expander is installed

Installation of turbo-expander in top gas line of

demethanizing column in naphtha cracking process

tnemevorpmiretfA krameR

yrevocertaehdloC 01x41.2 6 h/lack :sruohgnitarepO()y/h000,8srosserpmoctanoitpmusnocmaetsninoitcudeR h/t7.7


Before

Improvement

[Description

of

Improvement]

Improved section



Investment amount: 687 million yenImprovement effect: 137.4 million yen/yearInvestment payback: 5 years


[Practical Use]



170

Electricity

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1986

CN-ME-3

Table 1 Refrigerator power saving effect

In the naphtha cracking process, the bottom liquid of the demethanizing column is at a temperature of -30˚C andis fed to the ethylene rectificating column at a vapor/fluid ratio of 0.11. Since the increase in the vapor/fluidratio of the feed does not affect much to the efficiency of the ethylene rectificating column, the cold heat of thebottom liquid is utilized to reduce the power of the propylene refrigerator for energy saving.



The conventional process flow is shown below.

Fig. 1 Flow chart of demethanizing column and ethylene rectification column

Fig. 2 Flow chart of cold heat recovery from bottom liquid of demethanizing column

Cold heat recovery from demethanizing column

bottom liquid in naphtha cracking process

tnemevorpmiretfA krameR

taehdlocgnirevocerybrewopninoitcudeR y/hWk000,046,6 y/h000,8fonoitarepO


1) Two aluminum-made heat exchanger is Newly installed: one to the top vapor section of the depropanizingcolumn, the other to the feed chiller (refrigerator) of the demethanizing column. The bottom liquid of thedemethanizing column is flashed in the adiabatic mode using two control valves, and the cold heat is recov-ered, thus reducing the power of the propylene refrigerator.

2) The recovered power of the propylenerefrigerator is 830 kWh/h.

3) The flow after improvement is shownbelow.

Before

Improvement

[Description

of

Improvement]


Improved section




[Practical Use]



171

Fuel (steam)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1979

CN-ME-4

Table 1 Energy saving effect by reducing combustion-air preheating steam for boilers

In a naphtha cracking plant, hot water at the bottom of the cool-ing tower is cooled by process fluid to 60˚C, and further cooledto 35-50˚C using the cooling water (TW) before sending back tothe cooling tower. On the other hand, at the power plant boilers,the combustion air is heated to 240˚C using the 13 kg/cm2 steamand the boiler flue gas before sent to the boilers.

[Flow for utilizing process waste heat at boilers] (Refer to Fig. 1)

1) An air-preheater using waste heat from circulating hot water of the naphtha cracking plant was installedahead of the forced draft fan (FDF) for No. 1 and No. 2 boilers. Steam is no more used for preheating.

2) This improvement reduced the steam consumption by 13 t/h.





Fig. 1 Flow chart of combustion air preheating using process waste heat of cooling tower bottom hot water

Combustion air preheating for boilers using cooling

tower bottom hot water in naphtha cracking process


noitpmusnocmaetsninoitcudeR )h/t31(y/t000,401 y/h000,8:sruohgnitarepO


Improved section




[Practical Use]



172

Fuel (steam)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1979

CN-ME-5

Table 1 Energy saving effect by utilizing top vapor waste heat of distillation column

The top vapor of the CO2 stripper in this plant is at about 94˚C, and the top vapor of the MEG distillation

column is at about 105˚C. Both vapors are cooled by cooling water. On the other hand, in the “P” plant in thesame industrial complex, the bottom temperature of the rectificating column is at about 60˚C, and the reboileris heated by steam. This improvement is to circulate hot water along with the waste heat of the top vapor of therectificating column in the “B” plant, and utilize the waste heat as a heat source of the reboiler of the “P” plant.

1) It reduces the overall heat transfer coefficient to convert the cooling water to hot water at the top condenserof the CO

2 stripper. Accordingly, the internal structure of the condenser was modified.

2) As for the MEG distillation column, the pressure was changed from 25 to 36 Torr, and the top temperaturewas changed from 105 to 117˚C. After these modifications, a top heat exchanger was installed.

3) A condenser was installed at the B plant. A reboiler and a hot water tank were installed at the P plant.


“Energy Saving Journal (Vol. 37, No. 2, 1985),”P. 39


Fig. 1 Use of waste heat of top vapor of distillation column at reboiler by hot-water circulation

Hot water heating by distillation column top vapor

Principle

&

Mechanism

[Energy flow with B and P plants] (Refer to Fig. 1)

Fig. 1 Flow chart of heat among ethylene-oxide plant, B and P plants


noitpmusnocmaetsninoitcudeR y/t081,73


Improved section





[Practical Use]



173

Fuel

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1991

CN-OM-1

Table 1 Energy saving effect by controlling excess air ratio of cracking furnace

At this plant, a gas turbine generator was introduced, and its flue gas is used as combustion air for the crackingfurnace. Since the cracking furnace is operated under negative pressure, air is sucked into it. This improve-ment for energy saving is to control the excess air ratio using an oxygen analyzer mounted to each crackingfurnace.



Fig. 2 Flow chart for using gas turbine flue gas as combustion air

Principle

&

Mechanism

[Relation between fuel gas flow rate and theoreticaloxygen volume] (Refer to Fig. 1)

[Control of excess air ratio]The theoretical oxygen volume necessary for combus-tion is computed based on the molecular weight andfeed rate of the fuel, and compared with the oxygenvolume actually consumed for combustion. The feedrate of the air is controlled based on the theoreticaloxygen volume.

Fig. 1 Relation between the molecular weight and calorific

value of the fuel gas, and the theoretical oxygen volume

Control of excess air ratio at cracking furnace in



noitpmusnocygreneninoitcudeR 01x2.14 9 y/lack )secanrufgnikcarc51ottnelaviuqE(



Improved section




[Practical Use]



174

Fuel (steam)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1978

CN-OM-2

Table 2 Energy saving effect by changing feed step to depropanizing column

Conventionally the bottom liquid of the de-ethanizing column and the bottom liquid of the condensate stripperin the naphtha cracking process were joined and fed to the depropanizing column via the cooler. This improve-ment is to separately feed the bottom liquid of the condensate stripper to a lower step of the depropanizingcolumn, thus eliminating the use of cooling water for the cooler, and reducing steam consumption at thereboiler of the depropanizing column.

Fig. 1 Temperature profile of depropanizing column




Fig. 2 Feed system to depropanizing column

Principle

&

Mechanism

1) Conventionally, the bottom liquid of the de-ethanizing column and the condensate stripper were jointly fed toNo. 19 step of the depropanizing column.

2) The temperature profile in the depropanizing column is as shown in Fig. 1. After the improvement, thebottom liquid of the condensate stripper is fed to the lower No. 34 step.

3) At the same time, cooling water supply to the cooler in the feed line of the bottom liquid of the de-ethanizingcolumn is stopped. Thus, the steam consumption by the reboiler of the depropanizing column is reduced.

Table 1 Main components of bottom liquid of de-ethanizing column and condensate stripper

Change of feed step for depropanizing column in



noitpmusnocygreneninoitcudeR )h/t8.2(y/t006.91 )y/h000,7:sruohgnitarepO(

tnelaviuqelioedurcninoitcudeR y/Lk895.1

nmulocgnizinahte-eD reppirtsetasnednoC nmulocgnizinaporpeD

stnenopmocniaMC

3

C4

C5

%0.77%6.8%6.0

%4.32%2.94%4.22

erusserpgnitarepO mc/gk72 2 mc/gk01 2 mc/gk5.01 2

dohtemrefsnarT refsnarterusserP pupmuP


Improved section




[Practical Use]



175

Fuel (steam)

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1991

CN-OM-3

Table 1 Energy saving effect of pressure control of ethylene rectification column

This improvement is to reduce the refrigerator power by improving the control method of the propylene refrig-erator of the top condenser of the ethylene rectification column. This improvement was made at the time ofintroducing a decentralized control system (DCS) to the naphtha cracking plant.

Fig. 1 Pressure control method of ethylene rectification column





Fig. 2 Suction pressure control method of propylene refrigerator

1) A function to control the suction pressureof the refrigerator was added to the systemto control the pressure of the ethylene rec-tification column within the framework ofthe decentralized control system (DCS).Thus the heat transfer area of the condenseris now utilizd to the maximum degree.

2) As a result, the suction pressure of the re-frigerator was changed from 0.60 to 0.68kg/cm2G, and the power of the propylenerefrigerator was reduced by 250 kW.

[Pressure control method of ethylene rectification column] (Refer to Fig. 1)1) Before the improvement, the pressure of the ethylene rectification column was controlled by the liquid level

of refrigerant propylene in the top condenser.2) On the other hand, the suction pressure of the propylene refrigerator was controlled by the revolution speed

of the compressor.

Pressure control of ethylene rectification column by

suction pressure of propylene refrigerator in


tceffenoitcudeR krameR

rewoprotaregirferninoitcudeR h/hWk052ybdecudeRy/h000,7fosruohnoitarepO

tnelaviuqelioedurcninoitcudeR y/Lk524

Before

Improvement

[Description

of

Improvement]

Improved section

Improved section




[Practical Use]



176

Fuel (gas)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1979

CN-OM-4

This is the uniform O2 content combustion technology in the case that many burners are arranged in a singlefurnace. For the case of individual burners, refer to the Energy Saving Handbook, Equipment Common to AllIndustries, “Low O

2 Burners”.

Operation technology on uniform and low oxygen combustion of fuel gas for heating the ethylene cracker.


“Collection of Energy Conservation Cases1981,” p. 105, ECCJ


Through the above-described improvement (actions), the fol-lowing-listed effects appeared.(1)Horizontal distribution of O

2 content becomes almost uni-

form.(2)Vertical distribution of O

2 content is also improved as shown

in the right figure.(3)Fuel consumption is reduced as follows.

- Reduction by 30 Nm3/hBefore improvement 2190 Nm3/hAfter improvement 2160 Nm3/hReduction 30 Nm3/h

- Effect as amount: about 7 million yen (as 33 yen/Nm3)

Principle

&

Mechanism

Observation of distribution of O2 content in vertical and

horizontal directions in the furnace revealed the follow-ing. (1)Lateral O

2 content distribution is not uniform.

Left side: O2

1.5 ~ 1.7Right side: O

20.2 ~ 0.3

(2)Difference in O2 content exists in vertical direction.

Lower burner section: O2

7.0 ~ 5.0Upper burner section: O

21.0 ~ 0.7

Exit of convection zone: O2

1.2 ~ 1.0 (3) Actions - Primary air valve opening for burner is adjusted. - Primary air valve for each of lowermost row of burn-

ers is opened to a minimum necessary degree to pre-vent burning.

- For the third row and upper burners, also the secondary air valve is kept slightly open.

- Draft is adjusted to 3 to 3.5, somewhat stronger de-gree.

Ethylene cracker heats raw material naphtha to temperatures of from 800 to 850˚C to decompose into ethylene(thermal cracking). The cracker is an upright type with long depth, and has a radiation zone at lower partprovided with many burners (112 units) of short-flame radiation type at lower side walls, and a convection zoneat upper part (for preheating raw material and steam). The current combustion control values are: intrafurnacepressure at top of the radiation zone to a reduced pressure by 3 mm H

2O; and exhaust gas O

2 concentration of 1

to 3% (at exit of convection zone). Those control variables are checked by sampling from a single point over thewhole furnace. The fuel consumption for heating is 2,190 Nm3/h per furnace.

Energy saving in ethylene cracker

Many burners are arranged on the side walls,thus the side walls function as the radiationplane.

Naphtha cracking process

Improved section




[Practical Use]



177

Electricity

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1979

CB-ME-1

Table 1 Energy saving effect by heat-recovery generator

The top condenser of the ortho-xylene separating column in the aromatics production process is of an air-cooling type. The waste heat of the top vapor is dissipated from the air-fin cooler. The dissipated heat is as largeas 46,000,000 kcal/h and the temperature is 153˚C. This improvement is to recover this waste heat.

[Outline of heat recovery system] (Refer to Fig. 2)1) Through studying the use of a heat pump for generating a high-temperature heat source and the Ranking

cycle for recovering the power, power generation by a low-pressure steam turbine was adopted.2) The system comprises an evaporator, a feed-water heater, a steam turbine, a condenser, a condensate pump,

and a generator.

Chemical : BTX



[Balance of waste energy by form]

Fig. 1 Waste energy balance at ortho-xylene separation column

Fig. 2 Flow chart of waste-heat-recovery generator for ortho-xylene separation column

Recovery of top vapor heat of ortho-xylene

separation column in aromatics production process


Before

Improvement

[Description

of

Improvement]

ygrenederevoceR krameR

yticapacnoitarenegrewopegarevA Wk005,5 Wk005,6-005,4

noitarenegrewoplatoT y/hWM052,14 y/h005,7


Improved section

Investment amount: 720 million yenImprovement effect: 700 million yen/year (including the stoppage of one pump)Investment payback: 1 year


[Practical Use]



178

Fuel (steam)

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1983

CB-ME-2

Table 1 Energy saving effect by steam generation by heating-furnace flue gas

This process carries out secondary hydrogenation purification of cracked gasoline generated as a by-product inan ethylene plant. The heating furnace (recycle heater) heats the unreacted hydrogen from 340 to 500˚C. Theheating furnace was modified from natural draft type to forced draft type, thus improving its thermal efficiencyfrom 74 to 89.8%. At the same time, the heat of flue gas is utilized to generate steam. Thus, waste heat isrecovered with a significant energy saving effect.

[After improvement]

Chemical : BTX




Fig. 1 Flow chart of cracked-gasoline secondary hydrogenation process

Fig. 2 Flow chart of steam generation by recovered flue gas heat of heating furnace (recycle heater)

Waste heat recovery from heating furnace flue gas

in BTX production

tceffetnemevorpmI latoT

noitpmusnocmaetsninoitcudeR 01x12.0 6 h/lack y/Lk001,1)tnelaviuqeClioleufni(taehderevocerybnoitarenegmaetS h/t15.1



Improved section

Investment amount: 200 million yenImprovement effect: 23.2million yen/yearInvestment payback: 8.6 years


[Practical Use]



179

Electricity

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980

CB-ME-3

Table 2 Energy saving effect

At this plant, power is generated in-house using a bleeding-condensing turbine. Steam for production processesis the bleed from the turbine. Power balance is maintained by adjusting the condensing power generation.However, along with the progress in energy saving, steam consumption in the processes was significantlyreduced, and the condensing power generation nearly reached the upper limit. On the other hand, energy ofdistillation column top vapor of the xylene production process was not recovered. Therefore, a new condensingturbine was installed to recover power from the process, thus the steam to be generated by the old in-housepower generator was reduced, and the operation of one of the boilers was stopped.

Chemical : BTX



1) The top vapor (153˚C, 45 x 106 kcal/h) of the distillation column for separating ortho-xylene from mixedxylene in the xylene production process was formerly cooled by an air-fin cooler (AFC).

2) The 4th case among those studied was adopted to recover waste heat. The system comprises an evaporatorgenerating low-pressure steam (1.72 kg/cm2G) in parallel with the existing AFC, a condensing turbine powergenerator, and a feed-water heater.

3) Specification of the facilityCondensing turbine: 3-stage impulse-type turbine with adiabatic efficiency of 72%Generator capacity: 6,600 kW

4) System flow (Refer to Fig. 1)

- Case study for utilizing top vapor waste heat of distillation column (Table 1)

Fig. 1 System flow chart of steam-turbine power generation using top vapor of distillation column

Steam turbine power generation using waste heat of

distillation column top vapor in BTX production process

epyT dohtemyrevocertaehetsaW ymonocE snoitpodaroirP

noitaregirfernoitprosbA1 noitarenegretawdloC-ropavpoT KO ynaM

noisserpmocermaetserusserp-woL2-)noisserpmoC(-noitarenegropaverusserp-woL-ropavpoT

noitarenegmaetserusserp-muideMKO wefA

pmuptaeH3evirdenibruT-noitarenegmaetserusserp-woL-ropavpoT

)noitarenegyticirtcele,rewop(emoS enoN

enibrutmaetserusserp-woL4evirdenibruT-noitarenegmaetserusserp-woL-ropavpoT

)noitarenegyticirtcele,rewop(KO ynaM


tnelaviuqelioyvaehniygrenederevoceR y/Lk003,11 )sisabClioleuF(


Improvement

Study


Improved section



[Practical Use]



180

Fuel

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1977

CB-ME-4

Table 2 Energy saving effect by combustion air preheating

Combustion air preheating using heating furnace

flue gas in BTX production process

Chemical : BTX



1) The natural draft system was modified toa system using forced draft fans (FDFs)and induced draft fans (IDFs). Rotary-type air preheaters are installed.

2) As a measures to suppress NOx emis-sions, conventional burners were changedto low-NOx burners which assure stablecombustion even under a low excess-airratio.The low-NOx burner type: Voltmetricburner of sonic atomizing type

3) The result of the improvement is shownin Table 1.

This plant has three heavy-oil/gas fired reboilers for the distillation column and one gas fired furnace for thereaction-system charge heater. All of them are of a horizontal natural draft type. Accordingly, their flue gastemperatures were as high as 400 to 500˚C, and their thermal efficiencies were as low as 70 to 75%. Thisimprovement achieved the thermal efficiency of 88% by lowering the flue gas temperature through installingpreheaters for combustion air and employing mechanical draft.

Fig. 2 Flow chart of improvement by combustion air preheating using heating furnace flue gas

Fig. 1 Combustion system of heating furnaces (before improvement)

Table 1 Energy saving and environmental improvement data



ygrenederevoceR 01x5.8 6 )h/Lk49.0(h/lack )tnelaviuqeClioleufni(

*tnelaviuqelioedurcninoitcudeR y/Lk579,6

Note*: Heating furnace operating hours: 7,000 h/y

erofeBtnemevorpmi

retfAtnemevorpmi

tceffE

tceffegnivasygrenEybnoitcudeR

h/lk49.0

snoissimexOS m92.2 3N

h/ m91.1 3N

h/ybnoitcudeR

%84

snoissimexON m4.01 3N

h/ m1.7 3N

h/ybnoitcudeR

%23

Before

Improvement

[Description

of

Improvement]


Improved section

Investment amount: 100 million yenImprovement effect: 140 million yen/yearInvestment payback: 0.7 year


[Practical Use]



181

Fuel (steam), Water

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1984

CB-OM-1

Table 1 Energy saving effect by reducing amine circulation rate

Chemical : BTX



[Description of the process flow] (Refer to Fig. 1)1) The circulation rates of amine at V301, V302, and V303 were adjusted to optimal values according to the

respective feed gas flow rate of each column.2) The return water from V301, which was a cause of poor water quality, was re-routed so as to be directly fed

to V308. This change reduced the pure water feed rate.3) As a result, steam for the reboilers of V304 and V108 was reduced.

At this plant, sulfur-bearing gas generated as a by-product of BTX production by reforming is desulfurized. Asurvey of the current operation showed that the sulfur concentration in feed naphtha was in a range of 1/4 to 1/14 of the designed value. However, the circulation rate of amine as the absorbent of hydrogen sulfide wasmaintained at the excessive design level. This improvement is to reduce the circulation rate of amine, andreduce the steam rate to the reboiler of the amine regeneration column, eliminating a significant amount ofunnecessary energy input.

[Operating condition] - The design value of the sulfur concentration in feed naphtha : 1,400 ppm

Current operation data: 100 ~ 350 ppm - The circulation rate of amine (monomethanolamine) used to absorb hydrogen sulfide was at the design level.

Fig. 1 Flow chart of amine desulfurization process


Before

Improvement

[Description

of

Improvement]

Change of washing system in amine desulfurization

process for BTX production





Improved section



[Practical Use]



182

Fuel (steam)

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1976

CB-OM-2

Table 1 Energy saving effect by waste heat recovery

Chemical : BTX



[Flow after improvement] (Refer to Fig. 2)1) By increasing the heat transfer area of the heat exchanger for the top vapor of the crude benzene column by

three fold, the heat of condensation of the top vapor is utilized for preheating the feed crude light oil. Inaddition, the heat of condensation of the top vapor of the crude toluene column and the heat held by thecondensate of reboiler steam are utilized as the heat source of the reboiler of the pure benzene column.

2) To do this, a circulation pump for the reboiler liquid of the pure benzene column and a drain heat exchangerare newly installed.

This BTX production plant produces benzene, toluene, and xylene from light oil generated as a by-product ofcoke production. This improvement is to utilize heat of condensation of top vapor of the distillation column,heat held by condensate of steam used in the reboiler.

Fig. 1 Flow chart of BTX production around distillation columns (before improvement)

Fig. 2 Improved flow for reboiler heating by top-vapor waste heat of distillation columns


Before

Improvement

[Description

of

Improvement]

Reboiler heating by waste heat of top vapor of

distillation column in BTX production process





Improved section



[Practical Use]



183

Fuel (general) (steam)

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1979

CB-OM-3

(Before modification)

A unit to strip (separate) H2S dissolved in oil after hydrogenation of sulfur compounds (mainly thiophene) in a

benzene derivative production process.

Chemical : BTX


Modifications•The downcomer length was shortened by 17 mm.•The inlet weir was distanced from the downcomer by 18 mm.•The inlet weir was raised by 2 mm due to the fabrication convenience.

Waste heat recovery from heating furnace flue gas

in BTX production

1. The unit is a multi-stage deaerator to remove H2S by heating the oil with steam.

2. The operating pressure in a conventional system is 7.5 kgf/cm2G with heating steam of 10 kgf/cm2G.3. This unit is operated at 3.0 kgf/cm2G with heating steam of 5.2 kgf/cm2G.4. Thus, the unit enables to reduce steam consumption and steam pressure.

1. The safe operation range of the stripper is an area surrounded by the blowing (upperlimit), pulsating (lowerlimit), and flooding.

2. The requirements for modification are the following two items. •The cross-sectional area of the downcomer at each stage shall be sufficiently large in relation to the amount of liquid flowing down in the column, that is, the treatment capacity. •The gap between the bottom of the downcomer and the tray, and the gap betweenthe downcomer and the

inlet weir shall be adequate, and the pressure drop shall not be excessively high.3. Improvements to be made on a conventional stripper are; To enlarge the cross-sectional area of the downcomer

and the gap between the downcomer and the inlet weir. To enlarge the tray spacing (reduction of number of stages). To change the tray to a low pressure-loss type

(bubble cap tray to perforated tray).4. Configurations of strippers before and after the modification are shown below.

(After modification)

At a capacity of 300 t/d, the steam consumption, the steam pressure, and the stripping pressure are thefollowing.

Steam consumption Steam pressure Stripping pressure (kg/h) (kgf/cm2G) (kgf/cm2G)

Before modification 660 10 7.5After modification 535 5.2 3.0Effect 125

(accounting for ¥ 7,100,000 per year including the benefit of lowered steam pressure)


Improved section

“Collection of Energy Conservation Cases 1981,”Firs volume



[Practical Use]



184

Fuel (steam)

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1976

CB-OM-4

Table 1 Effect of control of reflux ratio of distillation column

Chemical : BTX



[Flow after improvement] Refer to Fig. 1

(1)The GC analysis values of feed are entered to the decentralized control system via an advanced controlsystem (ACS), and the control loop is changed to Fig. 1.

1)The quantity of benzene (FC-7) in the feed is determined using the feed analyzer (GC-1) and the flow meter(GC-1), thus controlling the quantity of crude benzene (FC-1).

2)Instead of the control of temperature inside of the distillation column, the internal reflux ratio control (RC-1) is adopted, and AC-1 is employed in the superior loop to control the toluene concentration in benzene toa constant level.

3)To the superior group of the temperature inside of the column TC-1, AC-2 is added to control the benzeneconcentration in the bottom liquid at a constant level.

(2)The result is the stabilized dispersion of toluene concentration, the reduction in reflux ratio, and the reduc-tion in steam consumption in the reboiler.

Since the operation control of the benzene distillation column in this plant was done by analog instruments,changes in feed rate and composition varied the toluene concentration in the product benzene, which raisedproblems in quality. The improvement is the introduction of decentralized control system (DCS) to the plant,and the adoption of reflux ratio control of distillation column under the on-line control, thus attains the reductionof steam consumption in reboiler.

Fig. 1 Control system of benzene distillation column after improvement


Before

Improvement

[Description

of

Improvement]

Control of reflux ratio of distillation column using

on-line analyzer

The operation is under a condition of excess value of reflux ratio of distillation column aiming to prevent thetoluene content in benzene from largely fluctuate owing to the changes of benzene concentration resulted fromfluctuation of feed rate of crude benzene to the benzene distillation column caused by upstream influence (dis-turbance) or from fluctuation of composition of feed.Furthermore, the bottom temperature of the column is set to higher level than normally expected value to pre-vent entering benzene into the residue.

tnemevorpmierofeB tnemevorpmiretfA tceffE

eneznebnitnetnoceneuloT mpp05±031 mpp01±081

tnemeriuqertinumaetsfonoitcudeR zB-t/gk805 zB-t/gk074 )%02(;zB-t/gk101ybnoitcudeR

)sisablioedurc(ygrenefonoitcudeR


Improved section



[Practical Use]



185

Electricity

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1980s ~

CG-PE-1

Gelatin which is widely used in photograph films, drugs, and foods is an extremely hygroscopic material, andthe drying of gelatin consumes large quantity of energy. The system is a case of energy saving as well asimproving the product quality by switching the conventional steam heat source hot air drying method to the heatpump method.

[Improved heat pump drying system] (Fig. 4) - Closed system of heat energy employs recycle of heat

not to generate waste heat.

Chemical : General

“Energy Saving Journal (Vol. 42, No. 4, 1990),”ECCJ Version


- Flow diagram of steam heating drying process - Flow diagram of heat pump drying process

Gelatin drying system using heat pump in

pharmaceutical production line

- Energy cost is reduced by 50%.An actual plant result: Conventional method: 52 million yen/yearHeat pump method: 26 million yen/year

Adopted at many sites. Japan Chemical Industry Association /ECCJ (JIEC)

Improved section

Improved section



[Practical Use]



186

Electricity, Fuel

Outline

Principle

&

Mechanism

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1990

CG-PE-2

This improvement significantly reduced fuel consumption by a heating furnace in a powder-detergent produc-tion line. When planning in-house power generation for peak power demand in the plant, a power generationsystem in which all the gas discharged from the gas turbine is recovered for reuse was adopted. The recoveredheat is used as heat sources for driers and other facilities for producing powder detergents for clothing.

[Gas-turbine specification]Gas-turbine generator: 750 kW, simple open cycle, single-axis typeFlue-gas temperature: 300-500˚C

“Collection of Energy Conservation Cases 1989,”p.1273


[Energy balance of gas turbine generator] (Refer to Fig. 1)

[Relation among fuel types, atomizing-air volume, and dust generation] (Refer to Fig. 2)When planning to use flue gas directly, its effect on the product quality needs to be checked.

Fig. 1 Energy balance of gas turbine

Gas-turbine energy efficiency: power generation (about 20%), waste heat recovery (about 75%), total 95%(Refer to Fig. 1)

Powder detergent drier utilizing turbine flue gas

Fig. 2 Relation among fuel types, atomizing-air volume,

and dust generation

Fig. 3 Flow chart of direct utilization of gas turbine flue gas for drier

Some sites adopting similartechnology.


Improved section

Detergent


Chemical : General


[Practical Use]



187

Electricity

Outline

[Description]

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1992

CG-ME-1

This improvement is to utilize a high-temperature heat pump for recovering waste heat of the alcohol distilla-tion column. The heat of condensation of top vapor of the distillation column, which was formerly wasted intocooling water, is recompressed by a screw compressor (VRC, MRC), and utilized to heat the bottom liquid ofthe column.

[Example of ethanol recovery from aqueous ethanol solution]1) As shown in Fig. 1, the vapor having a composition near to that of azeotrope (ethanol: 95.6 wt.%, 78.15˚C,

760 mmHg) is taken out from the column top, and the steam (73˚C, 265.3 mmHg) is generated by thecondenser/evaporator. The steam is heated to 816 mmHg (saturation temperature of 102˚C) using a screwcompressor (compression ratio of 3.08).

2) Since the facility gives a nearly zero alcohol concentration at the bottom of the column, the dischargedsteam can be directly injected, and no reboiler is necessary.

Buyo Gas Corporation “OHM (No. 6, 1988),” P. 49


Table 1 Energy saving effect by heat pump VRC

Fig. 1 Heat recovery system by steam recompression using heat pump at alcohol distillation column

Ethanol recovery unit using steam recompression

heat pump at alcohol distillation column

(Operating hours: 7,000 h/y)

metsyslanoitnevnoC CRVpmuptaeH tceffenoitcudeR

noitpmusnocmaetS h/gk006,1

noitpmusnocrewoP hWk361

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tnelaviuqelioedurcninoitpmusnoC y/Lk319 y/Lk772 y/Lk636fonoitcudeR


Improved section


Chemical : General


[Practical Use]



188

Fuel

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1986

CG-ME-2

Since the waste water generated in a phenol production plant contains phenol, acetone, and polymers of these,the biological treatment is difficult, and all of the waste water is incinerated by incinerators. Fuel consumed totreat the waste water accounts for about one third of the total consumption of fuel in the plant. This improve-ment is to reduce this fuel consumption.

[Flow of reverse osmosis membrane treatment] (Refer to Fig. 2)1) Waste water to be treated is 228 t/d from the oxidizer system, 125 t/d from the distillation system, and 72 t/

d from other systems. As the property of waste water from each system differs, several kinds of membraneswere tested.

2) It was decided that only the waste water from the distillation system is to be processed by the reverseosmosis membrane (RO membrane) after preliminary treatment. As a result, the volume of concentratedliquid to be incinerated was reduced to about one fourth. The treated liquid can be reused as a process wateras its phenol content was reduced,.

3) For reference, Table 1 shows the observed data of RO-membrane treatment of waste water from the distilla-tion system.

Some sites adopting similar tech-nology



Table 2 Energy saving effect by RO membrane

Table 1 Observed data of RO-membrane treatment of

waste water from distillation system

Fig. 1 Incineration of waste water of phenol plant

Description

of

Process

[Description

of

Improvement]

Reduction of waste water to be incinerated using

reverse osmosis membrane in phenol production

process

Fig. 2 Flow chart of RO-membrane treatment of waste water

from distillation system


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diuqil

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Improved section


Chemical : General


[Practical Use]



189

Electricity

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


Around 1994

Table 1 Comparison of energy saving effect and environmental improvement

In a conventional process for producing pharmaceuticals, the oxygen enrichment process adopted a vacuumconcentrator using a steam ejector. This improvement saved significant energy by switching the vacuum con-centrator to a membrane (ultra-filtration membrane) concentrator.

Tokyo Tanabe’s Ashikaga Plant“Collection of Improvement Cases at ExcellentEnergy Management Plants (1995)”

Conventional vacuum concentration using steam for oxygen enrichment had following problems.1) Instantaneous power failures or equipment troubles increased the liquid temperature, and generated a large

amount of poor-quality products.2) It required many types of equipment for the purposes such as heating, cooling, and evacuating, and they

consumed a large amount of energy. In addition, unmanned operation was not possible.

Evacuation-concentration system [Before improvement]

Before

Improvement

[Description

of

Improvement]

CG-ME-3


Improvement of oxygen enrichment process for

bulk pharmaceutical production

Ultra-filtration membrane system [After improvement]

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tnelaviuqelioedurcninoitcudeR y/Lk6.3


Improved section

Investment amount: 61 million yenImprovement effect: 32.7 million yen/yearInvestment payback: 1.9 years

Chemical : General


[Practical Use]



190

Electricity

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1992

Table 1 Energy saving effect by gas expander

In the feed-oxidizing reaction process for telephthalic-acid production, a large amount of non-reactive nitrogencontained in the air is emitted to the atmosphere. The temperature of the emitted flue gas varies with seasons:about 20˚C in winter and about 60˚C in summer. This improvement significantly saved energy by recoveringthe energy of the flue gas, which had formerly been dissipated to the atmosphere, using a gas expander (expan-sion turbine).


CG-ME-4


1) The flue gas has the energy of 36,000 m3/h and the pressure of 20 kg/cm2G.2) Gas expander specification

Expansion turbine: three-stage impulse-type (with heaters at inlet and intermediate stage)Generator : induction generatorOutput : 2,600 kWh/h

3) Power generation system (Refer to Fig. 2)

Power generation by turbo-expander in

telephthalic acid production process

Principle

&

Mechanism

[Description]

Fig. 2 Power generation system by gas expander (expansion turbine)

- The turbine rotor shall be made of SUS materials.


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noitpmusnocmaetsfoesaercnI y/t000,23 )h/t4(



Improved section


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tnemtsevnI)neynoillim(

tceffetnemsevnI)tceffE/tnemtsevnI(

)1( maetS+rednapxesaGrosserpmoc

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)2( obruT+rednapxesaGrosserpmoc

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)3( rewopllamS+rednapxesaGrotareneg

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[Selection of energy recovery system]

Table 1 Selection of a system to recover energy from flue gas

Chemical : General


[Practical Use]



191

Fuel (steam)

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1981

Table 2 Energy saving effect by waste heat recovery using heat pump

In this process, steam is introduced to the separator to heat and separate the solvent from the feed. The tempera-ture of vapor leaving the separator was about 90˚C, and this heat of condensation was wasted into the coolingwater at the cooler. This improvement for energy saving is to recover the waste heat in a form of hot water usinga heat pump, vaporize it in a flash tank, and reuse the steam at the separator.


The absorption heat pumps are classified into Class 1 and Class 2 as shown in Table 1 by the applicationmethod of waste heat.

CG-ME-5


1) A Class-2 absorption-type heat pump is installed in parallel with the existing cooler. Heat of condensation atthe cooler is 4.3 x 106 kcal/h.

2) The absorption heat pump recovers the waste heat of the cooler in a form of hot water (133˚C), from whichsteam (127˚C) is generated in the flash tank. The generated steam is supplied to the solvent separator. Thevapor condensed in the heat pump is separated into solvent and water in the drain tank. The separated wateris reused as make-up hot water for the heat pump.

Table 1 Classification and features of heat pumpsPrinciple

&

Mechanism

[Description]

Fig. 1 Flow chart of Class-1 absorption-type

heat pump

Waste heat recovery from solvent separator vapor

using absorption heat pump

in butadiene production process

Fig. 2 Flow chart of Class-2 absorption-type heat pump

applied to solvent separation process


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Improved section


Chemical : General


[Practical Use]



192

Fuel (general)

Outline

Structure

explanation,

Shape, and/or

System

diagram

Energy saving

effects

[Economics]

Equipment

cost

Remarks


1970s

Compared with a direct heating (high temperature oxidization) waste gas treatment facility, the fuel cost isdecreased to a level of 30 to 35%.

1) A catalyst to oxidize waste gas containing organic matters, tar generated in a furnace and hydrocarbons at alow temperature of 350˚C or below.

2) Oxidization decomposition allows to apply the catalyst for deodorizing, effective use of oxidization heat,and cleaning of waste gas, etc.

3) Low temperature combustion suppresses the thermal NOx generation

The Agency of Natural Resources and Energy,"Energy Conservation Setsubi Souran," P245,The Energy Conservation Center, Japan, 1986.

1) The supporting metals are Pt, Pd, or Rh.2) The catalyst effect enhances oxidization at a low temperature level (150 to 350˚C depending on the type of

gas).3) The operating condition is space velocity of 20,000 to 40,000 l/h, and catalyst bed height of 15 to 25 cm.

CG-ME-6


1) The catalyst is used in a shape of grain, honeycomb, foam, or fiber, depending on the operating condition.2) Following is an example of a catalyst system.

Principle

&

Mechanism

[Description]

Deodorizing and removal of harmful substances from waste gas of a chemical plant, oxidization cleaning of un-burnt gas and tar in an incinerator.

Low temperature catalyst combustor


Improved sectionSubstance

Operating

temperature (˚C)

Concentrationbefore treatment

(ppm)

Concentrationafter treatment

(ppm)


Chemical : General

11 chapter3 section3 chemical industry page137 192

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