Strategic Energy Management For Resilience

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Food Manufacturing Sector Energy

Efficiency

Salim Mirza

Senior Consultant, Energy Advisory

7th October 2015

Leveraging our global presence in different markets into local

competence to benefit clients for global impact

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400offices

105countries

16,500employees

150years

DNVGL’s purpose to safeguard life, property and the environment

further established with newly consolidated capabilities

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Energy Efficiency

in Food

Manufacturing

Introduction

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Common Utilities Deployed in Food Manufacturing Industries

Steam & Condensate - Different applications include in-direct heating for a variety of

heat exchangers for the process, direct/in-direct steam used for hot water generation

Hot Water – In some cases direct fuel fired hot water generators are also deployed

instead of using steam for hot water generation

Compressed Air - Commonly used as instruments for operation of pneumatic control

valves (temperature or flow control)

Introduction - Basic Steam Properties

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Components of an Industrial Steam

System

Steam Generation

Steam Distribution

Utilization

Condensate Recovery

Trapping

Basic Properties

Latent Heat

Saturation State – Saturated and

Super-heated

Dryness Fraction

Optimum Velocity for Distribution

and Utilization

• Rapid heat transfer through condensation

• Suitable for process heating applicationsSaturated Steam

• High degree of heat

• Suitable for power generation and special heating applications

Super-heated steam

Components of a Steam System in Food

Manufacturing Industry

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100% fuel

About 80% of Energy in form of saturated steam

About 77 % of energy availablefor process equipments

Process Consumption- About

57% Energy Gets

Transferred to The Process As Useful

Work

Energy Loss in Un-burntStack Losses &Blowdown

Condensate & Flash – About 22 % of energy which can potentially be

recovered to Feed Water Tank

Distribution losses – About 3 %

12 to 20%

Typical Issues in Steam Generation

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Optimum Generation Pressure

- Boilers are typically rated for steam pressures 10-15 bar (g) and above

- Some process applications need low pressure steam such as 4 or 6 bar (g)

- There is always a dilemma to decide an optimum generation pressure

Operate at Design Pressure and Reduce at Point of Usage

Better steam quality, higher thermal storage, better response to fluctuations, reduced

steam demand,

Increase in fuel consumption due to higher enthalpy is offset by the overall system benefits and productivity improvement

Operate at 4 bar (g) – lower then design and supply to process

Poor steam quality, water hammering, higher steam demand, reduced thermal

storage, poor operational control

Longer heating time, condensate evacuation problems, coil failures,

product quality issues

Steam Space

Water Space

Right Amount of Blowdown

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Key issues to consider

Safety

Energy efficiency

Avoids scale formation

When water evaporates

Dissolved solids gets concentrated

Solids precipitates

Coating of tubes/over-heating

Minimizes heat transfer

Large scale deposits can melt

Important Parameters to Address

Proper water treatment & blowdown practice essential

Always use treated water

Minimizes blowdown % in boiler

Aim for High Condensate Recovery Factor

Use de-aeration to remove the dissolved gases from feed water

Blowdown Percentage

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Boiler blow down % depends on

TDS content of feed water

Required TDS content in drum level

(governed by the boiler pressure)

Feed water TDS = 100 ppm

Boiler

Steam 10 TPHTDS = 0 ppm

Blowdown‘A’ TPH

TDS allowable= 3500 ppm

A x 3500 = (10 + A) x100

A = (1000/3400) x (1/10) x 100%

= 2.9% blowdown

Impact of Water Chemistry & Dissolved

Gases on Performance

The most harmful of the dissolved gases is oxygen, which can cause pitting of

metal.

Further the corrosion of iron forms soluble bicarbonate, which leaves no

protective coating on the metal.

If oxygen is also present, rust forms and CO2 is released, which is free to form

more corrosion.

Oxygen pitting and scale formation can destroy piping and boiler tubes as well as

interfere with heat transfer and the operation of PRV’s & trap mechanism.

Oxygen can be removed from the feed water, both by mechanical or chemical

deareation

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Critical Aspects for an Efficient Boiler

Operation

Excess air in flue gas

Combustibles in flue gas

Exhaust flue gas temperature (Waste heat recovery

depends on the Sulphur dew point)

Steam pressure

Fuel Quality

Feed Water Tank Management and Water Chemistry

Regulating Makeup Water

Enhancing condensate recovery

Removal of dissolved gases from feed water

Optimum Boiler blow down and Heat Recovery

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%

Air quantity

Excess airLess air

Excess Air Measurements in Oil/Gas

Fired Boiler

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Exhaust Stack

Boiler

FD fan

Economiser

Sampling

Point

FD fan Suction

Performance Assessment of Steam Boiler

Methods used : Direct efficiency and In-

direct efficiency

Direct efficiency = S/F ratio x (hg – hf)

GCV of fuel

Factors affecting direct efficiency

Variation in feed water temperature

Quality of fuel

Boiler loading %, on-off cycles, boiler

operation at lower than rated pressures

Blow-down losses

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Indirect Efficiency

Loss due to heat in stack

Enthalpy loss due to moisture in fuel

Un-burnt losses

Loss due to unburnt in flue gas

Radiation loss

Loss due to moisture in air

Air Infiltration Costs Money

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Disadvantages

Decreases flue gas temperature

Lower temperatures lead to metal corrosion

Increases quantity of flue gas, Leads to increase in power consumption

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ESP

ID Fan

FD Fan

SA Fan

Heat Recovery from Exhaust – Acid Dew

Point

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Case Study From a Food Industry – Feed

Water Tank Mass Balance

Present Heat and Mass Balance Across Boiler Feed Water Tank

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Feed water tank

Capacity – 15 kL

Level maintained – 75 %

Condensate -118252 kg/day @ 70 deg C

Make-up water quantity – 23982 kg/day @ 30 deg. C

Live Steam injected

6000 kg/day

Feed water – 148234 kg/day @ 88 deg. C to boiler

Case Study From a Food Industry – Feed

Water Tank Mass Balance

Proposed Heat and Mass Balance Across Boiler Feed Water Tank

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Feed water tank Capacity – 15 kL

Level – 75%

Blowdown - PHE

Possible Flash Steam recovery from blowdown - 976 kg/day

Make-up water - 18147 kg/day @ 30 deg. C

Feed water - 142234 kg/day @ 85 deg. C

Feed water – 142324 kg/day @ 87.5 deg C

Condensate from Machine A 5841 kg/day @ 95 deg C

Condensate from Machine B - 26040 kg/day @ 70 deg. C

Condensate from Other Plant Areas – 91230 kg/day @ 95 deg C

Blowdown water-

4064 kg/day @ 117 deg C

Live Steam injected @

6000 kg/day

Steam Distribution

Distribute steam at highest pressure

Smaller bore steam mains are required. The

smaller surface area means that less heat

(energy) is lost

Lower capital cost of steam mains and of

insulation (lagging).

Dryer steam at the point of usage because of the

drying effect of pressure reduction taking place.

The boiler can be operated at the higher pressure

corresponding to its optimum operating

condition, thereby operating more efficiently.

The thermal storage capacity of the boiler is

increased

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Saturated Steam – Typical Design velocity varies are in the range of 25 to 35 m/s

Flash Steam/ Low Pressure Steam –Typical Design Velocities are in the range of 10 to 15 m/s

Higher the velocity more will be the pressure drop in a given pipe size. The thumb rule for pipe sizing is to arrive at a balance between steam demand and pressure drop

Pipe Sizing

Over-sizing of pipe-work

The pipes will be more expensive than

necessary

A greater volume of condensate will be

formed due to heat loss

Poor steam quality and energy transfer due

to greater volume of condensate

Greater heat loss

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Under-sizing of pipe work means:

Higher steam velocity higher pressure drop thus

lower pressure than required at point of use

Not enough volume of steam at point of use

Greater risk of erosion and water hammer (and noise

pollution) due to increase in steam velocity

Pipe sizes may be chosen on the basis of either:

Fluid velocity or Pressure Drop / Both

In a particular example the cost of installing 80 mm pipe work was found to be 44% more than the cost of 50 mm pipe work which

would have had more than adequate capacity. The heat lost by the insulated pipe work was some 21% more from the 80 mm line

than it would have been from 50 mm. Any un-insulated parts would have lost some 50% more from the 80 mm size, than from 50

mm. This is due to the extra heat transfer area available.

Steam Utilization

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Steam Utilization should be at the Lowest Possible Pressure

Lower the pressure, higher the latent heat

Higher latent heat means higher rate of heat transfer and thus lower consumption

Results in reduced batch time

Lower pressure implies a lower steam flow rate for a given pipe size

There can be issues of steam starvation if pipe selection is not correct

The process temperature to be achieved should always be taken into account. As a thumb rule minimum steam temperature > Required Process Temp + 30 Deg.

Typical Steam Utilization in a Food

Industry

Majority of the steam is typically used for indirect heating equipments (likeevaporator, kettles and other different kinds of heat exchangers) and hot watergeneration.

Most of the steam used is for indirect heating applications for process heatexchangers.

Hot water generation also accounts for a major heat load

Important to ensure the right steam pressure in order to achieve the desiredprocess parameters as well as energy efficiency

Supplying too high steam pressure than needed results in excess energyconsumption.

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Steam Utilization – Case Study in Food

Industry

Efficient Hot Water Generation

Hot water used in Milk PHE, Ovens, Moulding Tank, Sugar Mixing Tanks

Method of Hot water generation

Direct steam consumption resulting in heat losses due to over-flow

Existing steam controls bypassed resulting in excess consumption due to temp over-shoot

Heat losses due to large sized tanks and water hold-up

Lag in availability of hot water should there be urgent demand

Improve efficiency of hot water generation using indirect generation with proper controls

Instantaneous hot water generation

Optimizing heat transfer

Condensate recovery

Better temperature control - Precision heat transfer

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Steam Utilization – Case Study of a Food

Industry

Potential of Improving Steam Economy in FFE

The operating feed rate is 6000 kg/hr

The designed evaporation rate is 4667 kg/hr

The actual operating evaporation rate is around 4500 kg/hr

The steam consumption is huge

Observed steam consumption is 2400 kg/hr v/s ideal steam consumption of 1617 kg/hr

Operating steam economy is 1.91 ( Ideal is 2.75, achievable is 2.5)

Triple Effect Evaporator steam consumption is high due to

Low vapor generation in first effect, inefficient recovery of low pressure (flash steam)

Thermovapour compressor (TVR) in the first effect is not operating as per design specifications

Temperature distribution across all effect need to be re optimized to design specifications

Steam consumption can be reduced to 1874kg/hr (saving 526 kg/hr of steam) through optimizing theexisting system

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Steam Trapping

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Steam traps perform the important function of holding back steam and allowingcondensate to pass through.

The selection is primarily based on the type of applications such as –

• For Steam Headers – Thermodynamic or Inverted Bucket Traps

• For Heating Applications – Ball Float Traps

• For Steam Tracing Lines – Balanced Pressure Traps

Common Problems in Steam Trapping

• Group trapping is the term used to describe the use of a single trap to drain

two (or more equipments)

• Improper trap selection – IB & TD type of traps being used for heating

applications

• Lead to waterlog and holdup of condensate

• Need to frequently open bypass valves thus leading to excess consumption

• Incorrect trap sizing

• Pumping condensate by trap pressure

• Trap stalling due to backpressure

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Common Issues in Steam Trapping

Trap stalling is the condition when the inlet steam pressure becomes less than the back-

pressure acting on the system. Thus, the condensate gets trapped inside the trap as there

is no positive pressure gradient available for flow

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This leads to hold up of condensate inside

the heat exchange leading to slow heating

rate, need to frequently open bypass

valves

This particularly is prominent for low

temp applications (below 100 deg C) and

where steam flow rate is regulated by

means of a control valve.

Commonly observed in food

manufacturing industries

Condensate Recovery

• Identifying potential for recovery

• Quality of condensate

• Maximizing condensate recovery, both in

terms of quantity and heat quality

• Proper utilization of flash steam

• Prevent holdup and multiple handling of

condensate

• Using energy efficient system for sending

condensate to feed water tank

• Maximizing Flash Steam Recovery &

Utilization

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Condensate (100 deg C)

10 kg/cm2

190 deg C

Flashvessel

Flash steam

Hot condensate

Summary

Steam Generation

Key areas to address – proper control of combustion parameters, excess air, blowdown

quantity, feed water tank management

Steam Distribution

Proper line sizing, routing, moisture removal, air venting, condensate recovery from

main lines

Normal distribution losses are in the range of 3 -5 % of generated steam

Steam Utilization

Achieve desired heat duty with optimum steam pressure, feasibility of reducing demand

by reducing losses, process modification, waste heat recovery.

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Condensate Recovery

Recovery of flash steam from HP condensate, avoid multiple handling and hold-up of

condensate, heat recovery from contaminated condensate

Trapping

Proper trap selection based on application, performance assessment of traps,

addressing steam loss from leaking traps

Summary

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THANK YOU

Salim Mirza

Salim.Mirza@dnvgl.com

+65-97238650