alcala de henares, spain steam and condensate …

GSK Manufacturing

Alcala de Henares, SPAIN

STEAM AND CONDENSATE ENERGY AUDIT REPORT

PROJECT N° 30284

1 Emission E. Morin R. Ivanov 06/04/2011 Item Description Established Checked out Date

STEAM AND CONDENSATE AUDIT

Project N°30284

GSK MANUFACTURING Alcala, Spain

Date: 06/04/2011

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To the attention of MM. Lopez and De Peña Established by E. Morin

TABLE OF CONTENTS

1 Executive summary ................................................................................................................... 4

2 Steam budget and summary of potential savings ...................................................................... 6

3 Optimisation project n°1: Improve energy production efficiency in the boiler house .................. 8

3.1 CURRENT SITUATION .............................................................................................................................. 8

3.2 OPTIMIZATION ....................................................................................................................................... 8

3.3 SAVINGS CALCULATION .......................................................................................................................... 9

3.4 INVESTMENTS ...................................................................................................................................... 10

4 Optimisation project n°2: Reduce steam pressure on Hot Water heat exchangers + install a

pumping trap ................................................................................................................................... 11

4.1 CURRENT SITUATION ............................................................................................................................ 11

4.2 OPTIMIZATION ..................................................................................................................................... 12

4.3 SAVINGS CALCULATION ........................................................................................................................ 13

4.4 INVESTMENT ........................................................................................................................................ 14

5 Optimisation project n°3: Improve steam ancillaries insulation ............................................... 15


5.2 OPTIMIZATION ..................................................................................................................................... 16


5.4 INVESTMENTS ...................................................................................................................................... 16

6 Optimisation project n°4: Isolate the old condensate return line ............................................. 17


6.2 OPTIMIZATION ..................................................................................................................................... 18


6.4 INVESTMENT ........................................................................................................................................ 20

7 Summary of deviations noticed during the audit ...................................................................... 21

7.1 STEAM GENERATION ............................................................................................................................ 21

7.2 STEAM DISTRIBUTION ........................................................................................................................... 21

7.3 STEAM USERS ..................................................................................................................................... 23

7.4 CONDENSATE RETURN ......................................................................................................................... 25

8 Complete check list of all verifications done during the audit ................................................... 27

9 Recommended complementary studies................................................................................... 29


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9.1 ADDITIONAL ENERGY-SAVING OPTIMISATIONS ........................................................................................ 29

9.2 ADDITIONAL OPERATIONAL OPTIMISATIONS ............................................................................................ 31

10 Appendix N°1: Determination of the 2010 boiler house efficiency ............................................ 32

11 Appendix N°2: Steam consumption calculations – all users .................................................... 36

11.1 DESIGN DATA ...................................................................................................................................... 36

11.2 REAL CONSUMPTION SIMULATION (MAXIMUM) ........................................................................................ 37

11.3 REAL CONSUMPTION SIMULATION (MINIMUM) ......................................................................................... 39

12 Appendix N°3 : Steam Pressure Controlled Heat Exchangers at Low Load ............................. 41


12.2 OPTIMIZATION ..................................................................................................................................... 44

12.3 SAVINGS ............................................................................................................................................. 46

12.4 INVESTMENTS ...................................................................................................................................... 46


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1 Executive summary

The energy audit conducted from March 21st till March 24th 2011 by Armstrong covers the 4 parts of

the steam loop: boiler house, steam distribution, steam consumption and condensate return.

GSK factory located at Alcala de Henares, in Spain, produces medicines as liquids, tablets and

sachets.

Steam is mainly used by:

- Coils to heat air around 40-60°C in fluid bed dryers and coaters

- Heat exchangers for hot water production at 65°C (sanitary water, HVAC and CIP)

Hot water can also be produced by 2 gas-fired hot water boilers (581 kW each). Generally one boiler

is started during 2 months in winter. The rest of the time, the boilers are stopped.

Steam is distributed at 7 barg from the boiler house.

In some locations, steam pressure is reduced to 4 or 2,5 barg.

Steam is produced by one gas-fired steam boiler (1394 kW – 1,96 tons/hr). You have a second

identical boiler as back-up.

Steam production during the audit was about 450 kg/hr (2 steam users were shut down for

maintenance operations). However we estimate the factory average steam consumption between

600 and 1500 kg/hr depending on the season.

Our calculations based upon data collected during the audit show a 2010 steam price of 37,5 € per

ton and an annual steam budget estimated at 108 400 €.

Some steam and condensate lines are undersized considering design data of steam users.

Insulation of pipes is correct, however several steam ancillaries should be also insulated.

The steam distribution system is under trapped, especially in front of control valves and in “low

point”, resulting in a serious risk of steam leaks caused by corrosion, erosion and water hammering.

All Condensate that could be recovered is sent back to the boiler house using 3 pumping traps units.

Condensate return ratio was calculated to be 91% all over the year.


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No steam trap survey has been carried out during the audit as it has been done last October. Your

trap population is about 25 traps. 3 of them was reported leaking and 1 was not installed properly

(reversed). You did replace the failed traps recently.

The savings calculated for optimization projects in this report were based upon engineering

assumptions, observations and standard engineering practices.

We estimate the potential energy savings of at least 8% of the estimated steam budget, which

represents a yearly saving of about 170 MWh, 29 tons of CO2 and 8990 €.


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2 Steam budget and summary of potential savings

The boiler house is composed by 4 boilers: 2 identical fire-tubes steam boilers and 2 hot water

boilers.

Most of the time, only one steam boiler is running. The others are stopped except during the coldest

weeks in winter.

Energy metering is being developed but currently the factory has only one gas meter for the whole

boiler house. It is therefore not possible to know the gas consumption for hot water boilers when

they run.

According to data provided for 2010 we estimate:

Boilers steam generation:

• Total yearly steam generation in 2010: 1987 MWh (2890 tons/year)

• Steam cost in 2010 : 54,5 €/MWh (37,5 €/t)

• Total yearly steam budget in 2010 : 108 400 €/year

• Efficiency estimated: 88% (see calculation in appendix n°1)

• Steam cost foreseen in 2011 for same production level : 47,1 €/MWh (32,4 €/t)

Basic data considered:

• Gas unit costs : 41,12 €/MWh hhv for year 2010

35,23 €/MWh hhv since February 2011

• Gas High Heating Value : 42.1 MJ/Nm³

• Water costs :

o 2 €/m³ for city water

o 5030 €/year for Chemicals


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Steam consumption repartition:

According to operating hours registered for 2010 and estimated steam flows for each user, the

repartition of the consumption for 2010 is the following:

Summary of identified energy-saving optimizations and their estimated yearly results:


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3 Optimisation project n°1: Improve energy production efficiency in the

boiler house

3.1 Current situation

As calculated in appendix n°1, the normal steam production efficiency is estimated at 88%.

There is no heat recovery existing on stacks or blowdown.

Moreover, the steam boiler load is directly affected by the weather as about 56% of steam is

produced for hot water to HVAC.

When outside temperature is getting warmer, the boiler load is decreasing.

When energy demand of steam users is lower than the minimum capacity of the burner, the boiler

starts cycling: the burner stops, steam pressure decreases and when the lower point is reached, the

burner restarts. However during this phase, a period or purging with ambient air inside the fired

tubes is necessary. This purging causes energy losses.

Therefore too much cycling of the burner, due to low load, will decrease the steam production

efficiency.

During summer, we estimate your average steam need for the factory at about 250 kg/hr (see

appendix N°2) which lead to a steam production efficiency loss of 4% (due to cycling losses mainly).

3.2 Optimization

In order to improve the global steam production efficiency, we propose to:

- Use a smaller steam generator (about 850 kg/hr) modulating from 20 to 100% equipped with an

economizer on stacks. Steam production efficiency would be at least 92%

When the steam demand will increase in winter (due to the use of defrosting coils and low

outside air temperature), you can restart the existing steam boiler to increase your capacity.


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- Use hot water boilers all over the year to produce hot water for HVAC and Cleaning (Sanitary

water) : 92% efficiency

This configuration will improve the global efficiency of energy production during a major part of the

year.

3.3 Savings calculation

Savings due to the improvement of steam production efficiency during 6 months per year:

SAVINGS CALCULATION for steam generation

Steam production efficiency in summer 84%

Energy demand (factory only) (spring + summer) 385 MWh/year

Corresponding gas consumption 509 MWh hhv/year

Costs 17928 €/year

CLAYTON STEAM GENERATOR efficiency 92%

Energy produced 385 MWh/year



FUEL SAVINGS 1559 €/year

CO2 savings 2,6 t/year

Savings due to the production of hot water with hot water boiler instead of steam boiler:

SAVINGS CALCULATION for hot water generation

Current steam production efficiency 88%

Energy demand (Hot water only) 1.218 MWh/year



Hot Water boiler efficiency 92%

Energy produced 1.218 MWh/year



FUEL SAVINGS 2355 €/year

CO2 savings 3,9 t/year

WATER Treatment (chemicals) SAVINGS (estimated) 3000 €/year


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Total savings for this optimization would be 6900 €/year.

3.4 Investments

The budgetary cost for the optimization is 70 000 €.

This cost includes:

- A New steam generator (Clayton EOG-60, 589 kW, 820 kg/hr) with economizer

- 24 hours self operation

- Installation and commissioning

The second steam boiler currently used as back-up is not necessary anymore therefore the budget

can be reduced by 50% by selling 1 existing steam boiler.


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4 Optimisation project n°2: Reduce steam pressure on Hot Water heat

exchangers + install a pumping trap


Two shell and tubes heat exchangers, located in the boiler

house, produce hot water at 63°C for HVAC and cleaning

(sanitary water).

These exchangers are fed with 7 barg steam.

We also noticed some slight water hammers in the condensate

return line.

Indeed on the same return line are connected condensate

from both heat exchangers and a drip trap from the 7 barg steam line.

Depending on the load of heat exchangers, condensate can accumulates and cool down at 65°C

while other is hot. This will generates water hammering and risks of damages for the installation.

Temperature measurement on Sanitary hot water exchanger:

Steam boiler shut down – gas failure


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Red = steam inlet (after control valve) and Blue = condensate outlet (before steam trap)

Temperature measurement on HVAC hot water exchanger:

4.2 Optimization

Considering the temperature setting of hot water, these 2 heat exchangers could be fed by 3 barg

steam.

The latent heat at this pressure is higher than at 7 barg, which allows reducing the steam

consumption for hot water production.

Moreover, as shown in the measurement above, at low load condensate can accumulate in heat

exchangers. To help evacuating this condensate at any operating conditions and avoid water

hammering, several solutions exist (see appendix N°3).

Considering your situation, we recommend to install a mechanical condensate pump as described

below:


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This is optimization will save about 2400 €/year.

4.4 Investment

The budgetary cost for the optimization is 4000 €.

Including:

- Installation of 1 pressure reducing valve

- Move of the condensate pump from the Aeromatic dryer technical area to the boiler house

(linked to project n°4).


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5 Optimisation project n°3: Improve steam ancillaries insulation


Not only for safety reason, must hot surfaces have effective insulation to

prevent excessive heat loss by radiation. The basic function of insulation is

to retard the flow of unwanted heat transfer. There is more chance of part

of steam to condense during distribution if the pipelines are not properly

insulated.

There is a closely interrelated efficiency between boilers and their

distribution systems. The losses occurred in the distribution systems have

a significant impact on boiler operations. When these losses are minimized, boiler plant efficiency is

improved.

We observed some valves on steam lines which are not insulated in your steam distribution system.

The following table shows the non-insulated equipments identified during the audit:

Location Ancillaries length or DN Pressure loss

type number (mm) (barg) (W)

GLATT defrosting coil valve 1 25 7 365

Dryer Aeromatic valve 1 65 7 865

Dryer Aeromatic valve 1 65 7 865

Distribution to factory (new line) valve 2 65 7 1731

Technical area / offices valve 2 65 7 1731

Technical corridor - CIP valve 1 50 7 652

The total radiation loss is calculated at 5844 W.


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5.2 Optimization

We recommend installing insulated jackets on all ancillaries located in

steam lines above DN25. These jackets are easy to remove in case of

maintenance operations.


SAVINGS Calculation

Total radiation losses 5844 W

Operating hours 5232 h

Annual loss (time corrected) 32,5 MWh/yr

Steam production efficiency 88% (lhv)

Annual primary energy loss 36,9 MWh lhv/yr

Annual primary energy loss 41,0 MWh hhv/yr

Fuel cost 35,23 €/MWh

Annual financial loss 1445 €/yr

CO2 emissions 7,5 t CO2/year

Savings calculated are 1445 €/year.

5.4 Investments

Budgetary cost for this project is 2100 €.

Including:

- On site measurement to prepare tailor-made manufacturing of the jackets

- Supply of insulation jackets

Payback time for this optimization is less than 21 Months.


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6 Optimisation project n°4: Isolate the old condensate return line


During the audit, we could not find any updated drawing with the condensate lines and we were not

able to follow all condensate lines in the factory because some of them were not accessible.

However we suppose the network is the following:

In the factory, there are 3 pumping traps allowing sending condensate back to the boiler house:

- One connected to the coater 350

- One close to the Aeromatic dryer

- One in the technical room near the offices

Depending on the back pressure, condensate can return to the boiler house following 2 ways: the

new connection to the boiler house or the outdoor rack.

AC48

AC350 CIP GLATT

Aeromatic

Boiler house

Pump

Pump

Pump

DN20

DN25

DN25

DN40

DN40

DN25

Outdoor rack

Outdoor ra

ck


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The condensate pump located in the technical room near Offices needs steam as motive fluid. As

nowadays steam is coming exclusively from the factory and not from the outdoor rack anymore,

several meters of steam line is still in use only for this application.

6.2 Optimization

There is no need to keep 2 ways to send condensate back to the boiler house. Besides it implies a

loss of energy by radiation.

We recommend isolating the condensate return line and the steam line, the closest to the branch

from CIP/GLATT/Coaters line.

The pumping trap located in the technical room near offices can be moved to replace the one close

to the Aeromatic dryer as its capacity is bigger (DN40 against DN25).

AC48

AC350 CIP GLATT

Aeromatic

Boiler house

Pump

Pump

Pump

DN20

DN25

DN25

DN40

DN40

DN25

Outdoor rack

Outdoor ra

ck


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Savings calculation is based on radiation losses by un-needed condensate lines and steam line.

Condensate pipes have been considered with 30 mm insulation and steam pipe with 40 mm

insulation.

Savings would be around 630 €/year.


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6.4 Investment

The budgetary cost for the optimization is 2600 €.

Including:

- Insertion of isolating valves

- Move of the condensate pump from Offices technical room to the Aeromatic dryer technical

area.


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7 Summary of deviations noticed during the audit

7.1 Steam generation

Water costs

Considering your city water last invoices and the quantity of chemical products purchased in 2010

for water treatment in the boiler house, the total cost for 1 m³ of treated water is 21,99 €.

This price seems to be really expensive.

With Nalco, you have decided to change the chemical product type, this may help reducing the

amount of chemicals needed and will reduce the treated water costs.

7.2 Steam distribution

Missing condensate drain points

Poor drainage of steam lines will cause accumulation of condensate in the steam distribution

system, especially in “low point”, thus causing a serious safety hazard for water hammering.

Also on some locations there are no drip legs installed on steam lines in front of control valves.

When these valves are in a closed position condensate will accumulate in front of these control

valves, and sub-cool. This sub-cooled condensate is aggressive (low PH) and will cause corrosion

of the valves and piping. Also there is a risk for thermo shock and water hammering. Furthermore

accumulated condensate will compromise steam quality and cause early wear of piping and

ancillaries due to erosion.

Some examples:

Steam distribution – near CIP Mix water/steam- GLATT GSW

Steam distribution – outlet boiler house

Defrosting coil – Coater 350


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Note that if you improve the condensate drainage of steam lines, it will contribute increasing general

condensate return temperature (currently 80°C in the condensate tank). It will therefore improve

your steam production efficiency as feed water temperature entering the boiler will be higher.

Steam line size

From the boiler house, 2 main lines distribute steam to users:

- 1 to feed the 2 heat exchangers to produce hot water, size = DN65

- 1 to feed the users in the factory, size = DN65

Design consumption for the hot water production is 1016 kW or 1780 kg/hr 7 barg steam.

Design consumption for the factory current users is about the same: 1029 kW – 1786 kg/hr 7 barg

steam.

As the table above shows, each steam line is a little bit undersized. This may induce higher pressure

drop and increase noise.

For good operating conditions, steam flow should be less than 1380 kg/hr in each steam line:


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In winter we estimate the maximum steam consumption for the factory at about 1330 kg/hr and hot

water production should not exceed a steam consumption of 1220 kg/hr if one hot water boiler is

started in the coldest weeks.

In conclusion, the design steam consumption is almost never reached in the existing situation;

therefore no problem is expected till the steam usage is not increased for production reasons.

7.3 Steam users

Steam users in the factory are:

- 2 fluid bed dryers (Glatt WSG360 and Aeromatic)

A first steam coil is used in winter to prevent from freezing and a second coil heats the air between

40°C and 60°C (depending on the recipe).

We noticed a steam leak in the Glatt defrosting coil. It must have been broken during the winter.

The Glatt dryer also use a mixing valve to produce hot water at 65°C for cleaning. This is the only

point of losing condensate. However this equipment is not often used.

The temperature setting point of hot air is quite low: less than 60°C. Thus steam coils may operate

often at low load and the steam pressure after control valves may be below atmospheric pressure

(<100°C). Therefore there will be no driving force (pressure differential) available to push the

condensate out of the coil and move it to the condensate return lines. The condensate will back up

Defrosting coil – Glatt WSG360

Defrosting coil – Aeromatic


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in the coil and will become flooded. This situation can lead to water hammering. (see appendixes

n°3).

For the Aeromatic dryer the situation is improved by the mechanical

condensate pump. This equipment will help reducing the return line back

pressure and therefore the condensate evacuation.

However for the Glatt dryer we haven’t seen a condensate pump directly

linked to the condensate outlet line.

- 2 coaters (48 and 350)

Coaters also use 2 coils to heat outside air (defrosting and heating).

The temperature setting range is the same as the dryers. Therefore same flooded situations may be

observed.

The coater 350 (Manesty) steam system is equipped with a mechanical condensate pump but not

the coater 48 which is directly linked on the condensate main return line.

On the coater 48, we also noticed that condensate from the 2 coils is drained by the same trap.

Depending on the load of the 2 coils, this configuration may generate condensate accumulation and

water hammering. Each coil fed by a different control valve should be trapped by a specific steam

trap.


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- 1 CIP unit with air dryer

This unit is used by a cleaning cabin. CIP water at 60°C is spayed in the

cabin for cleaning and hot air (80°C) is then blown for drying.

The water is heated by a vertical tube and shell heat exchanger.

A vertical heat exchanger always works flooded, thus condensate may be at

low temperature (close to the product setting temperature) and some water

hammering in condensate return lines can be generated.

7.4 Condensate return

Condensate lines size

Considering the design steam consumption, we think that some condensate lines are undersized.

Indeed condensate line from CIP, coaters and Glatt is in DN25 for 1400 kg/h condensate. If we

consider a low steam pressure after control valves (1 barg), the calculation is the following:


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It will increase the back-pressure in condensate line of minimum 22 mm WC per meter of pipe.

However, considering the current situation, this undersized design will not disturb your condensate

system.

Pumping trap Coater 350

The piping configuration on the pumping trap near the coater 350 is the following:

The pumping trap is not working at atmospheric pressure as the equalizing line is connected to the

condensate inlet.

This configuration works, however we would recommend moving the 2 condensate lines from drip

traps to the main return line after the bypass valve. Indeed the equalizing line should never be

flooded in order to assure the pumping trap cycling.

STEAM 2.5 bars

CONDENSATE

CONDENSATE RETURNDrip trap

Coater coil

Coater coil

Drip trap

Equalizing line

Pumping

Trap


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8 Complete check list of all verifications done during the audit

Potential optimisation Status Comments

STEAM GENERATION

Steam pressure setting OK Maximum steam pressure setting for the boiler is

13 barg. Operating at 7 barg is a good

compromise. Operate at lower pressure may lead

to risk of carry-over in the boiler

Feed water temp. to the boilers To be improved Measured temperature of feed water entering the

boiler is only 70°C. It should be around 80-90°C

minimum.

Stack temperature in front of

economizer

To be improved Stacks temperature is between 180 and 230°C.

Stack temperature after economizer NA There is no economizer to recover energy from

stacks.

Combustion air temperature OK Ambient air in the boiler house.

Oxygen rate OK Between 3 and 6% depending on the firing rate.

Boiler sizing To be improved Refer to project 1

Boiler blow down rate OK Reported to be around 3% the last 2 months

Deaerator pressure NA

Feed-water pre-heating NA

Boiler stand-by time and volatility of

steam demand

To be improved At low load (specially in summer time),boiler

efficiency may be decreased by 5%

Boiler blow-down recovery NA


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STEAM DISTRIBUTION

External leaks of steam or condensate

from pipes, flanges, etc.

OK No important leaks have been observed.

System design, trapping points etc. To be improved Missing drip legs in “low points”

Insulation OK Few valves should be insulated also

Steam quality To be improved Add some drainage point on steam lines will help

improving steam quality

Steam pressure level OK

Water hammering OK

STEAM USERS

Condensate drainage and air venting

from heat exchangers

OK

Steam traps To be improved 5 traps were not tested during the last trap survey.

Steam traps should not be insulated.

CONDENSATE AND FLASH STEAM RECOVERY

Condensate recovered OK

Sizing of condensate return lines To be improved

Flash steam recovery NA

Water hammering To be improved Water hammers have been observed in

condensate line from the hot water heat

exchangers in the boiler house


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9 Recommended complementary studies

9.1 Additional energy-saving optimisations

Replace steam by hot water:

The highest temperature needed by current steam users is 80°C, but most of temperature settings

are about 60°C. Therefore the usage of 7 barg/170°C steam is questioned.

As heating fluid, hot water at 80-90°C could be sufficient.

Moreover your factory already owns 2 hot water boilers.

Hot water production efficiency by these boilers is about 92%. By using steam, it is maximum 88%.

For the same energy production, savings would at least 4% on gas consumption +make-up water

consumption and chemicals :


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This is only energy savings. Remove steam will also lead to maintenance savings.

However, a problem of design needs to be highlighted. Hot water boilers capacity is 581 kW each,

which means a maximum energy production of 1162 kW.

If we gather all design data from current steam users, the sum of energy needed is about 2045 kW.

If we do the same calculations but with real temperature settings, the result is closer to the hot water

boilers capacity but still higher (1226 kW), especially in winter time (Refer to appendix N°2 for

calculations).

In conclusion the current design of hot water boilers is not sufficient to replace steam. A third hot

water boiler would be necessary.

Besides, to get rid of steam in the factory also implies to:

- replace all steam coils by hot water coils in coaters and dryers

- install a new hot water network distribution with several pumps


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9.2 Additional operational optimisations

Flooded heat exchangers:

Poor drainage of condensate from low temperature controlled heat exchangers could have an

impact on productivity (decreased heat exchange surface and unstable heating temperature) and on

maintenance (leaking heat exchangers due to corrosion and water hammering). The reasons for this

phenomenon and possible solutions are described in details in appendix 3. Almost all anti-freezing

coils on dryers and coaters equipments are operating under these conditions. In case flooding of

heat exchangers starts creating important productivity and maintenance problems, we recommend

studying in more details the best solution for each concerned heat exchanger.


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10 Appendix N°1: Determination of the 2010 boiler house efficiency


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11 Appendix N°2: Steam consumption calculations – all users

11.1 Design data

TOTAL Steam consumption 3567 kg/hr 2045 kW

Fluid bed dryer Aeromatic

Fluid bed dryer GLATT

Design data

Estimation design

defrosting coil 31,35 kW

defrosting coil 30 kW

steam pressure 7 barg


steam consumption 55,1 kg/hr


air flow 10000 m³/h

air flow 2700 m³/h

estimated design delta T 60 °C

estimated delta T 60 °C

Energy needed 184,9 kW






Total steam consumption 370,9 kg/hr


Coater 350

Coater 48

Design data

Estimation



steam pressure 2,5 barg




Heating coils (2) 176,0 kW

air flow 7040 m³/h

air flow 4000 m³/h











CIP unit

Hot Water Production HVAC

Design data

Water flow 37,5 m3/h

Heat exchanger 348 kW

Temperature IN 40 °C


Temperature OUT 60 °C


Energy needed 871 kW

Dryer (coil) 46,4 kW



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air flow 1884 m³/h




Hot Water Production Sanitary


Water flow 2,6 m3/h








11.2 Real consumption simulation (maximum)

TOTAL Steam consumption 2129 kg/hr WINTER 1226 kW

TOTAL Steam consumption 1182 kg/hr SUMMER 685 kW

Fluid bed dryer Aeromatic


Design data

Estimation








air flow 2700 m³/h












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Coater 350

Coater 48

Design data

Estimation








air flow 7040 m³/h

air flow 4000 m³/h











CIP unit

Design data

Hot Water Production HVAC winter









air flow 2153 m³/h






Hot Water Production HVAC summer




Temperature IN 62,5 °C



Energy needed 22 kW










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11.3 Real consumption simulation (minimum)

TOTAL Steam consumption 1205 kg/hr WINTER 725 kW

TOTAL Steam consumption 751 kg/hr SUMMER 465 kW

Fluid bed dryer Aeromatic 249


Design data

Estimation








air flow 2700 m³/h











Coater 350

Coater 48

Design data

Estimation








air flow 7040 m³/h

air flow 4000 m³/h











CIP unit

Hot Water Production HVAC winter

Design data










air flow 2153 m³/h




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Hot Water Production HVAC summer




Temperature IN 62,5 °C



Energy needed 22 kW










NOTA : the CIP unit is a big consumer in terms of instantaneous steam flow. However this user only

runs 3 hours per day as an average. Therefore, its consumption has to be considered as a peak of

consumption.


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12 Appendix N°3 : Steam Pressure Controlled Heat Exchangers at Low

Load


Within the steam system, there are several pressure controlled heat exchangers operating at low

loads. Within these heat exchangers, liquids or gasses (air) are heated along with the steam. Most

of the time the desired medium temperature is below 100°C, and the heat exchanger is working at

partial load. Under these conditions, regardless of brand or model, problems may occur due to the

physical properties of the steam.

An audit is only a short visit on site, in which it is impossible to see all operating conditions. Most

problems with heat exchangers only occur at certain conditions. For instance, operation of heat

exchangers for building heating may only be a real problem during the fall and the spring, when

partial loads are typical. Due to the variability of these problems they are often not recognized in

time, and can cause process bottlenecks, loss of production, loss of temperature control and

increased maintenance costs.

Control of steam pressure can be designed in two ways: modulating or on-off. In both cases the

control valves are modulated by the measured temperature of the heated media. Steam pressure

controlled heat exchangers at low loads almost always produce sub-cooled condensate.

Modulating Controls

The steam pressure after a modulating control valve is always lower than the steam pressure in the

up steam lines, unless the system is working at full load which is a rare operating condition.

When heating a product to a temperature below 100ºC, the required steam temperature will often be

close to 100ºC, as the latent heat of the steam is used to transfer the energy as the steam

condenses. Steam temperatures lower than 100ºC, has a pressure below atmospheric pressure. If


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the steam pressure after the steam control valve is less than the pressure in the condensate line,

there will be no driving force (pressure differential) available to push the condensate out of the heat

exchanger and move it to the condensate receiver. The condensate will back up in the heat

exchanger, and will become flooded. This situation is often called a “stall situation”. As the

condensate backs up in the heat exchanger, it will exchange sensible heat with the product, where

the condensate becomes sub-cooled (matching the product temperature). The infrared pictures

below show the condensate backing up in a heat exchanger and the resulting temperature

differences in it.

The more a heat exchanger is oversized, the sooner it will operate at a partial load and the more

the condensate will sub-cool.

In the best case scenario the control system will balance the steam/product differential. However, in

most cases the following is observed:

Due to the condensate backing up the amount of heated surface in the heat exchanger is reduced,

and the desired set point product temperature cannot be reached. As a reaction to this, the steam

control valve will open, thus providing enough pressure differential to push out the condensate.

When this happens all the heating surface in the heat exchanger is available again causing a

sudden rise in the product temperature. There will be an overshoot in temperature which the


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controls will try to correct by closing the steam control valve. This cycle will repeat and control valves

will “hunt” searching for balance. Hunting control valves, and actuators, wear quicker and tend to

leak. The most critical aspect of cycling control valves is that the frequent changes in temperature

will cause local material stresses in the heat exchanger, which over time can cause failures and

leaks (especially in stainless steel). In addition the presence of relatively cold condensate may

cause water hammer and corrosion inside the heat exchanger which can also lead to leaks.

Lowering the condensate back pressure will reduce the risk of condensate backing up in the heat

exchanger, which provides two system improvements. First, it will reduce the loss of exchanger

capacity, and second, it reduces the risk of water hammer. Often when condensate is backing up,

the condensate lines are drained to the sewer. This is only a temporary fix and is a great loss of

energy and can raise waste water temperatures above safe limits.

On-off controls

As with modulating controls, very similar conditions occur in an on-off control. The steam valve

opens when there is a heat demand. A positive pressure differential is created, and the condensate

in the heat exchanger is pushed out. The heating surface in the heat exchanger is exposed and the

capacity rises. Before all of the condensate is pushed out, the desired temperature is reached and

the steam valve closes. During this cycle the steam trap does not receive condensate with a

temperature above 100ºC.

When the steam valve closes, the steam in the heat exchanger will condense, thus creating a

vacuum in the heat exchanger. This vacuum will pull condensate back from the condensate line

unless there is a check valve in place. The condensate inside the heat exchanger will continue to

cool down (sub-cool). When the steam valve opens again, the hot steam will be in contact with the

relatively cold condensate. When this occurs there is a serious risk for thermal water hammer to

occur. Over time these water hammers, and the presence of cold aggressive condensate, can cause

leaks.

Installing a vacuum breaker and a check valve may eliminate the vacuum and the backing-up of

condensate, but it will also allow air to enter the system. This air has to be vented from the heat


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exchanger otherwise it will reduce the effective steam temperature, and as a result, the heat

exchanger’s capacity. Air in the condensate system will cause corrosion.

12.2 Optimization

A number of solutions have been developed to solve the problems with heat exchangers at

low/partial loads. Finding the most effective and efficient solution would require custom tailored

engineering. Basically there are three methods to remove the condensate from a flooded heat

exchanger with steam pressure control:

• a closed loop pumping trap

• a Posipressure system

• a safety drain trap

A closed loop pumping trap arrangements uses a balancing line to equalize the pressure in the heat

exchanger and the pumping trap. Condensate will drain by gravity toward the pump, and will be

pushed out using steam pressure. The diagram below shows a typical setup:


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A Posipressure system allows air or nitrogen to push out the condensate as soon as the steam

pressure inside the heat exchanger is less than the back pressure in the condensate system. The

diagram below shows a typical setup for this arrangement:

A safety drain is a second trap that is sized to handle the same load as the primary trap. It is

located above the primary trap and discharges into an open sewer. When there is sufficient

differential pressure across the primary trap to operate normally, condensate drains from the drip

point, through the primary trap, and up to the overhead return line. When the differential pressure is

reduced to the point where the condensate cannot rise to the return, it backs up in the drip leg and

enters the safety drain. The safety drain then discharges the condensate by gravity.


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12.3 Savings

The installation of closed loop pumping trap systems, or a Posipressure system, will return

condensate back to the boiler house. Often on flooded heat exchangers this condensate is drained

to sewer and therefore lost. It can increase the heat exchangers capacity, and may speed up

production processes. More important are the savings achieved from improved system reliability

and controllability, however these are often difficult to quantify. The safety drain will not improve the

condensate return, but will save the coil from freezing and prevent process time downs and

maintenance labour to repair.

12.4 Investments

Average budgetary cost for the installation of a closed loop pumping trap system on an existing heat

exchanger is 14000 €.

Average budgetary cost for the installation of a Posipressure system on an existing heat exchanger

is 8000 €.

Average budgetary cost for the installation of a Safety Drain on an existing heat exchanger is 1700€.

Included:

- Equipments supply (piping, pumping trap / Posipressure, valves etc. )

- Installation by a mechanical contractor

- Engineering and project management

Payback time for these optimizations depends on the specific situation.

alcala de henares, spain steam and condensate …

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