Resources

Section : A | General Information about important utilities.

• Steam Distribution Networks
• Boiler
• Boiler Selection:
• Before selecting type, capacity and pressure of the boiler it is necessary to understand max steam flow and pressure required for the process including future requirement and losses through system.
• After ascertaining max. steam demand it needs to understand variations in steam flow with respect to time and min and average flow rates should be arrived at.
• Based on the flow pattern, capacity and quantity of the boiler/s can be fixed.
• For selecting boiler type in terms of fuel on which it will run, no. of passes, construction type like smoke tube packaged or bigger water tube boiler depends upon various no. of. factors such as availability of fuel, space, flow and pressure requirement, initial and operating cost, supply and erection time etc. These needs to be weighed against each other on project specific basis.
• An oversized boiler will operate at lower efficiencies and hence will result in increased fuel consumption.
• An undersized boiler will cause starvation of steam consuming processes.
• Two small boilers as against one big boiler working continuously will be less efficient steam generation system.

• Boiler parameters:
• Boilers capacity is specified in terms of F & A 100 Deg. C this means that,

            For example if any boiler is of capacity of 1000 Kg/Hr. F & A 100 Deg .C then it will produce 1000 Kg/Hr. of steam at atmospheric pressure from 1000Kg of feed water               at 100 Deg. C. Hence before specifying boiler F & A capacity factors must be considered based on feed water temperature.

• Efficiency of  the Boiler:

             Boilers efficiency is measured in two ways direct efficiency and indirect efficiency.

Where,

Q= Steam Generation Rate in Kg/Hr.

H= Enthalpy of Steam in Kcal/Kg.

h= Enthalpy of Feed Water in Kcal/Kg.

q= Fuel feeding rate in Kg/Hr.

GCV=Gross calorific value of fuel in Kcal/Kg.

With this method plant people can evaluate quickly the efficiency of boilers since it requires few parameters for computation and less instruments. However this method does not give details about where the loss is happening and hence corrective action to be taken. If dryness fraction of the steam is not known then this method can lead to inaccuracies.

Comparatively method of calculating boiler efficiency by indirect method considers more no. of parameters and gives an idea about the parameters which is affecting boiler efficiency.

Indirect Efficiency of boiler as per BS-845 in % =

100 – (L1+L2+L3+L4+L5+L6+L7+L8)

Where,

L1= % Heat loss in dry flue gas.

L2= % Heat loss due to partial conversion of C to CO.

L3=% Heat loss due to un-burnt in fly ash.

L4=% Heat loss in bottom ash.

L5=% Heat loss due to hydrogen in fuel.

L6=% Heat loss due to moisture in air.

L7=% Heat loss due to moisture in fuel.

L8=% Heat loss through surface

Note: For Gas & Oil fired boilers L3 & L4 is not considered

• Dryness Fraction of Steam:

• Feed Water:
• Ideally feed water should be heated up to 100 Deg C to remove oxygen completely.

             Presence of oxygen in the boiler feed water causes corrosion of boiler internals as well as plant equipment and pipelines.

• Indicative characteristics of boiler water,

Note: These are just indicative parameters, for accurate parameters respective boiler manufacturer should be consulted with.

• Feed Water Tanks:

            Feed water tank is an important element of boiler house. Feed water tanks capacity should be minimum 1.5 times of the max. steam generation for an hour. Feed                  water tank should have necessary mountings like level gauges, level switches, De-Aerator head (for proper mixing of condensate, flash steam and make-up water.                  Proper heat balance of feed water tank must be carried out to ascertain how much condensate and/or flash steam can be admitted to the feed water tank                                Excess  flash steam or condensate can boil feed water content causing unsafe vibrations of the feed water tank.

• Fuel:

             Adequate fuel should be stored inside the plant based on the fuel consumption, conditions of supply and logistics facilities.

• Fuel Storage:

• Bulk storage of all petroleum products should be done carefully as per the Petroleum Act.
• That means sufficient distance should be maintained from main factory building/ process house/ utility house. Within the tank farm area also sufficient distances should be maintained between fencing and boundary wall in between two tanks, between storage and pumps and between pumps and unloading area. There should be dike wall around the tanks of such a height that it is forming sufficient volume to accommodate oil stored inside the tanks.
• Some viscous fuels like F.O. need heating to keep them fluid, since at ambient temperature these types of fuels tend to become semi solids. Pipelines conveying these kind of fuels also need heating in the form of steam or electrical tracing.
• Base coil heating systems as well as heat tracing of F.O. pipelines has to be designed proficiently for safe and satisfactory operation.
• Right type of fire extinguishing equipment should be installed near the tank farm and to be checked for satisfactory operation periodically. Fire extinguisher van should reach the oil storage area easily.
• All electrical panels, motors should be provided with flame proof enclosure.

         For all gaseous fuels,

• Fuel comes at a termination point within the factory premises from gas distributing authority. At this place there is one metering station is installed and from there gas pipeline is taken to users within the plant like boiler, burners etc.
• In the pipe work of such fuels special care needs to be taken in selecting pipeline material supporting, selecting valves and workmanship.
• Right type of fire extinguishing equipment should be installed near metering and usage points.
• All Solid fuels (Wood, Coal, Pet coke, Bagasse, Briquette)

           Agro Residues (rice husk, coconut shells, groundnut shells, coffee husk, Wheat stalk)

             Should be stored in covered, cool and dry place.

• Right type of fire extinguishing equipment should be installed near storage area.
• Preferably conveyors should be used to transport fuel from storage to boiler feeding systems.
• Proper sizing of fuel should be done to achieve efficient combustion.

• Energy monitoring/savings in Boilers:
• Some typical Steam to Fuel ratios:
• Oil/Gas = 13 to 16
• Solid Fuel= 3 to 5
  • 1 Deg. C increase in feed water temperature can reduce fuel consumption by approximately 3 to 4%
  • Steam loss through an orifice Kg/Hr

• Steam distribution Network
  • In steam distribution network steam pipelines should be correctly sized. If a steam pipeline is lower than the correct size it causes excessive pressure drop and process doesn’t receive required pressure. This may further lead to incomplete heating, longer process time.
  • If the steam pipeline is higher than the correct size capital cost goes high, for bigger steam pipeline network increase in capital cost can be sumptuous. Higher pipe size then required also caused higher heat losses through the steam network. Hence it is necessary to select a correct steam pipeline size for the given flow.

• Condensate Recovery Network

• By increasing feed water temperature fuel consumption can be reduced drastically. To achieve this all clean process condensate must be recovered as well as condensate getting generated from all the steam pipelines should be recovered. Increase in condensate recovery eventually increases feed water temperature and reduces make-up water consumption. Similarly flash steam also should be recovered since it has almost same amount of heat as it is in the condensate from which it gets generated.
• Feed water temperature can be further increased by heating it by using any heat present in any other source such as heat in flue gases of any directly fired system, through properly designed economizers, through blow down of boiler, through hot effluent etc.
• For any kind of heat recovery system it is necessary to understand, what will be the payback for heat recovery systems? How much heat can be added to the feed water tank? What should be the design of any heat recovery system?
• Properly designed condensate and flash steam recovery system is crucial for achieving,
• Higher steam to fuel ratio.
• Saving in make-up water consumption.
• Saving in make-up water treatment cost.
  • Proper condensate recovery system can be put in place by selecting correct size and type of trap, correct size and placement of condensate pipelines and right type of condensate recovery pumps.
  • Condensate and flash steam recovery system needs to be monitored on continuous basis specially for checking health of the traps.

• FAQs about the boiler & steam;
• Should the boiler run at lower pressure then it is designed for?

Boiler should not be operated at lower pressure then it’s designed operating pressure. Because at lower operating pressure specific volume of the steam increases and causes mixing of water particles with steam producing wet steam. Because of this wet steam is produced which causes longer process times. If at lower operating pressure then designed, dry steam is to be produced then steam generation rate will reduce which may not suffice process requirement.

• My boiler’s feed water pump is not able to maintain normal feed water level inside the boiler, feed pump capacity is correct for the steam being produced?

Probably your boiler is generating wet steam. This is causing large amount of water being carried along with the water which is not being cope up by feed pump. Wet steam is produced because of smaller drum size then required for the boiler to generate dry saturated steam, Boiler internals are damaged, surge demands, problem with chemical treatment of boiler.

• Chimney of my new boiler has stated corroding very early what could be the reason for this?

Flue gas contains SO2, this SO2 condenses if flue gas temperature goes below the Dew point of SO2 inside the flue gas. When the SO2 condenses and comes in contact with water Sulfuric acid gets formed and which corrodes chimney rapidly. To avoid condensing of SO2 velocity, temperature and infiltration of air should be controlled. Temperature at which SO2 should exit of boiler chimney depends upon SO2 contain in flue gas. Flue gas temperature drops along the height of the chimney as it goes towards outlet of the chimney hence sometimes top portion of chimney is lined with SS sheet.

• What is clean steam?

Clean steam is the steam which is used in pharmaceutical industry for direct heating purpose like in sterilizing autoclaves.

• How the clean steam is produced?

Clean steam is produced in a clean steam generator, which is exchanger which uses black steam to evaporate pure water to form clean steam.

• Is it necessary to check steam traps of the plant frequently?

Yes it is very much necessary to check steam trap periodically since. After certain amount of operation traps can fail, around 18% trap stark leaking means passing the live steam, 5% trap fail in closed position and around 13% start malfunctioning.

• What is Flash Steam?

When high pressure condensate come at atmospheric pressure at the outlet of trap then it’s temperature changes to the saturation temperature at atmospheric pressure. Excess energy existing in the condensate due to difference in it’s temperature before trap and after trap is utilized in evaporating some amount of condensate in steam which is called as flash steam.

Flash steam contains almost same amount of energy as it is in the condensate from which it is generated. Hence it is important to recover flash steam also. Flash steam get’s generated at the outlet of each trap like line trap, process trap except in the cases where sub cool condensate generates like in the steam tracing applications. Flash steam generated from the boiler blow down also can be recovered.

• Compressed Air Distribution Network.

1. • Compressor Selection:
     • Compressor capacity and pressure selection method is similar to that of boiler’s.
     • Based on the flow pattern, ambient temperature at site & RH of site location,

Capacity and quantity of the compressor/s can be fixed.

• Out of major compressor types available like screw, centrifugal, reciprocating selection of right type of compressor is often governed by Flow range, Pressure required, Operating and running costs, space required.
• Selection of compressor room accessories such as Filters, Dryers and Air receivers should be done on the basis of air quality required, dryness requirement and air flow.
• Details of air classes are defined in standard BS ISO- 8573

• Efficiency of Compressor

2.2.1)  Isothermal Efficiency of Compressor= Isothermal Power/ Input Power

• Compressor Room Layout:

2.3.1)       Compressor room must be located where adequate clean dry and cool air supply to the compressor can be maintained.

2.3.2)       Sufficient space should be available for moving around compressor and it’s accessories for inspection, operation and maintenance purpose.

• Compressed Air Parameters:
• Compressor flow is defined as free air delivery commonly termed as FAD.

             This flow is air flow at the suction of compressor. At the discharge of compressor volume of the air is reduced due to compression and it can be derived by dividing FAD by compression ratio.

• Most of the time flows given by users are also on FAD basis and hence that can directly be used for compressor capacity selection after due confirmation. However pipelines are sized for compressed air flow.
• Typical power consumption for different types of Air Compressors:

             Centrifugal: 0.16 KW/CFM, Oil Lubricated Screw: 0.17 KW/CFM, Oil Lubricated Reciprocating: 0.18 KW/CFM

• Energy monitoring/saving in Compressed Air System:

2.5.1)     1 Kg reduction in generated pressure of compressed air can reduce power consumption by 7%

2.5.2)     Typical losses through various dia. Holes in compressed air system at 6 Bar (g) operating pressure.

• FAQ for Compressed Air Systems,

2.6.1)     What is breathing Air?

Breathing air is required in pharmaceutical industries or chemical industries, where there are chances of contamination of air within room rendering it not fit for breathing. Hence separate system for breathing air is put in place with dedicated compressors and filtration system. Breathing air apparatus are installed in each clean room through which air can be provided for breathing. This air is to class D as per OSHA norms.

2.6.2)     What are the avenues available in compressed air network for saving energy?

In a compressed air system energy can be saved with some basis steps such as,

1. Reducing leakages (It is found that in poorly maintained plant compressed air leakages can be as high as 20%).
2. Generating compressed air at exact pressure as required by the process.
3. Proper sequencing of compressors and avoid short cycling.

• Process Water Distribution Networks

3.1         Process Water Pumps

3.1.1)     Pump Selection:

• Selecting of pump capacity is similar process as to selecting boiler or compressor.
• Flow and pressure requirement govern selection of type of pump amongst commonly available pumps/pumping systems such as centrifugal pump, reciprocating pump or pressure boosting system.
• Calculating correct head of pump is very critical because generating higher pressure then required by the process will increase energy consumption and on the other hand inadequate generation of head will not suffice process requirement.
• Understanding process pressure & flow requirement, pump NPSH requirement and NPSH available are some of the key elements which need to be understood and defined for satisfactory operation of the pumping system.

3.1.2)     Pump Efficiency is calculated by,

• Work Done by Pump = Q x ρ x g x h
• Where Q = Flow in Cum/Sec
• ρ=Density of the fluid ( Kg/Cum)
• g= Specific Gravity (9.8 m/S^2)
• h= Head delivered by Pump (m)

3.2         Layout of Pumping Station

Pumps should be placed in such a way that there is safe distance available for moving around for monitoring, operation & maintenance. There should be sufficient distance available for removing motor, pump etc.

3.3         Energy efficiency in pumping system;

3.3.1)     If the system is working on throttled valve at user point or, water flow is required to be by passed then pump is oversized. In this case if the load is constant it is better to reduce the pump capacity by trimming impeller, reduce pump RPM. If the load is variable then installing VFD can be a solution.

3.3.2)     In centrifugal pumps as per the law of affinity between pump speed, flow and power absorbed

Q α N; H α N^2; P α N^3

Where,

Q= Pump Flow Rate; N= RPM; H= Pump Head; P= Power absorbed by pump

Hence if flow and head are kept exactly as per the requirement then power consumed by the pump can be saved.

3.3.3)     In order have efficient pumping system,

• Pumps should be selected and operated near to the best efficiency point.

Reduce pressure drop in the system.

• Cater small high pressure requirement by separate booster pump, and utilize lower head pump for normal pressure requirement.

• Chilled Water Distribution Network

4.1)        Chiller Selection:

There are different types of chillers available Major types are,

Chillers working on Vapor compression refrigeration cycle

Chillers working on Vapor absorption refrigeration cycle

Chillers working on Vapor compression refrigeration cycle are subdivided in to type of compressors used as well as cooling method,

Based on the compressor type:

1) Reciprocating

2) Scroll

3) Screw

4) Centrifugal

Based on the cooling method

1) Air cooled

2) Water Cooled

3) Evaporative cooling.

Water cooled type chillers can be used with more benefit where there is requirement of hot water process. Evaporative type of chillers are more efficient then air cooled chillers and Water cooled chillers are most efficient. Where waste steam or hot water is available at such places Vapor absorption chillers are the most economical choice.

4.2)        Efficiency of chillers is measured in terms of COP which stands for coefficient of performance.

COP = Cooling Power/ Input Power

4.3)        Chilled Water Circulation Network,

4.3.1)     Chilled water is circulated in following different manners as per the process requirement.

• Constant flow chilled water system.
• Primary only variable flow design.
• Primary secondary variable flow design.
• Hot Well & Cold Well circulation system.

4.3.2)     In chilled water circulation or any kind of circulation for that matter flow to each user has to be balanced. That means even distribution of the flow to the equipment nearest to chilled water pump to the farthest equipment. This is achieved by providing balancing valve on the return line of the equipment. Selection between manual or automatic balancing valve can be made based on the criticality of the process.

4.4)        Properties of chilled Water:

For process temperatures above 10 Deg C, normal water can be used as chilled water.

For temperature less than that Glycol solutions are used.

• Cooling Water Networks

5.1)        Cooling Towers

Cooling towers are used when water is required near wet bulb temperature. Cooling towers are available in different types and sizes.

Depending upon draft

1) Natural Draft

2) Induced Draft

Depending upon flow of air and water w.r.t. each other

1) Cross flow

2) Counter flow

Bases on the requirement and other criteria such as initial and operating cost optimum selection can be made.

• Nitrogen

Nitrogen is required as a purging gas for blanketing of some chemical reactions.

It is also used for packing food to prevent it from degrading.

Nitrogen is generated by two methods,

• Pressure Swing adsorption

Grade: A- 99.95% Pure Nitrogen

• Membrane type N2 generators

Grade: B- 99.5 %Pure Nitrogen

Note: All the information given above is for general information purpose only. For actual design of