Steam Boiler: Steam Boiler Component

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Requirement Design of Tubes

Requirement design of tubes is made to make sure design tube can be used in certain temperature and pressure in steam boiler. Tubes are one pressure parts. These provisions should apply to any tubular pressure part that is either exposed over much of its length to hot gases for purposes of heat transfer or is directly butt welded to such a tubular pressure part.

Requirement design of tubes should comply with the requirements of the ASME Boiler and Pressure Vessel Code, Section I, Power Boilers. The calculation of tube thickness should be based on ASME BPV Section I.

The requirement design of tubes should describe the design basis for controlling mechanical wastage (eq. grit and soot blower erosion) and chemical wastage (e.g. fireside corrosion, dew point corrosion) of tubing. During the design phase, the requirement design of tubes should supply details of the wastage provision for each tube design.

Membrane panel construction should be either by a fusion welded fin or integral fin method. Resistance welded fin construction will not be allowed. No tube bend should contain a circumferential weld. Parallel down-flow circuits subject to significant variations in heat absorption and/or resistance to flow between these circuits should be avoided. A staggered arrangement of tubes in the gas pass should not be used.

Durable caps suitable for transportation should be provided on each end of the tubes to prevent damage and rust on inside surface of tube and to prevent entry of debris. Corrosion or erosion margin of tube thickness should be provided for the boiler tubes.

Design Header in Steam Boiler

Design header in steam boiler should comply to ASME Boiler & Pressure Vessel Section I (ASME BPV). Header shells can be manufactured by a seamless process. Feed water connections to drums should be of a thermal sleeve design unless an alternative design is agreed with the owner.

Headers should be provided with access arrangements to allow full internal visual inspection and cleaning. Wherever possible, the access openings should be through header ends and should be arranged in order that the numbers of inspection openings are minimized. The openings shall have an internal diameter of at least 75mm in order to allow televisual inspection of the complete header.

The closure of these openings should be of a permanent type, fixed by means of fully penetrating butt welds with suitable length allowance for future cutting and re-welding.

All headers which are designed on a time dependent basis should be fitted with creep pips or other means, to allow periodic measurement of diametric creep distension.

All nozzles, branches and tube stubs should be attached by welding and should be of the set on type. The weld preparations and welding procedures should ensure fully penetrating welds. Reinforcing pads should not be used.

No nozzle, branch or tube stub weld shall encroach over the heat affected zone of main seam welds. Any specific instances where these requirements cannot be complied with should be submitted to the Purchaser for approval during the design phase.

All nozzles, branches and tube stubs shall be of a sufficient length to ensure adequate access for welding on the adjoining tubes or pipes and to permit effective post weld heat treatment of these butt welds so as not to affect the integrity of the drum / headers.

Design header in steam boiler should be performed to ensure safety during operation. Diameter, thickness and material to be used should be calculated as per design

Design Steam Drum and Water Drum

Design steam drum and water drum is important step in design steam boiler due to mechanical design and performance design. Steam drum and water drum are two of pressure part in boiler. The steam drum should be furnished with internals which at least include hydraulic baffle, mesh dryer screens to meet the required steam purity, and blowdown connection. Also, the drum internals are protected from any possible attack by the chemicals and there is no chance of chemicals short-circuiting and being discharged through the continuous blowdown system.

The water drum size is dependent on the number of tubes deep in the boiler bank. The chemical feed connection could be located on the water drum. By placing the chemical feed on the water drum the chemicals combine with the circulating water and are better mixed before entering the steam drum.

The drums should be of fusion welded construction fabricated from carbon steel plate and should be equipped with 450 mm diameter manholes on both end plates of the drum to permit access into the drum interior. All faces between manholes and drum plates should be fabricated and machined so as to obtain a perfect seal.

Necessary welding end inlet and outlet connections and nozzles are provided to accommodate the required valves and accessories. Steam drum should be provided with the necessary connections, such as safety valves, continuous bIowdown, water level and pressure measuring instruments, vents, etc.

Sufficient thermocouples should be provided on the drum shell. The metal temperature should be measured as input data to the plant computer which should be furnished in the computer room.

All connection openings should be protected with caps before shipment. Drum should be capable of complete drainage so as to assure the dry preservation of boiler when not in service. Pipes carrying the saturated steam from the boiler drum to the superheater should be evenly spaced on the drum and designed so that an adequate distribution of steam will be obtained for the superheater.

Necessary drum supports, such as U-bolts and nuts, should be furnished. Continuous steel rings for insulation support around manholes should be welded on the drum. Two (2) multiple port type drum water level assemblies, two (2) level transmitter pressure gauges and other necessary accessories should be provided on the drum. Boiler water level should be indicated on operator monitor in the central control room.

Insulation and jacketing should be installed on boiler drum and necessary fittings should be assembled and welded in the manufacturer's shop before shipment. Field welding of parts or fittings should be minimized. A single pass - cross flow or multiple passes generating bank design should be furnished. The generating bank should employ a 400 mm central access cavity for maintenance.

The tubes are rolled during erection into the steam and water drums without any butt welds. The entire generating bank sidewall construction features finned tubes will eliminates the need for an inner casing. Where header/drum ends are attached by welding this should be by using a fully penetrating plain butt weld joint.

Drums and headers should be self draining and provided with drain valves. Design headers / design steam drum and water drum material should be in accordance with ASME Boiler & PV SectionII D.

Ash Handling Equipment in Stoker Boiler

Ash handling equipment in stoker boiler is one of parts on ash handling system in a power plant unit. Ash is the product of coal combustion in stoker boiler. It should be discharged to maintain well combustion in the furnace.

There are some ash handling equipment are installed in stoker boiler such ash chute hopper, air plenum hopper, ash cooler, ash conveyor, and the equipment of ash handling can be mechanically, hydraulically, and pneumatically.

Bottom ash from the travelling grate is discharged through the ash chute hoppers installed at the end side of travelling grate as shown in Figure 1. The manual sliding damper is installed at each bottom of the air plenum hoppers. The air plenum damper should be opened minimum once per day to exhaust the riddling ash. And opening interval should be adjusted according to the condition of the quantity of riddling ash. Before open the damper, wheelbarrow should be prepared under the damper.

Figure 1: Traveling Grate Ash Handling Equipment

Fly Ash Handling Equipment

Fly ash collected at fly ash hopper at the bottom of tubular air pre-heater and multi cyclone that discharge by butterfly damper and rotary damper accordingly as shown in Figure 2.

Figure 2: Fly Ash Handling Equipment

Fly ash re-injection system

Fly ash from boiler bank hopper and economizer hopper that contains un-burned coal dust is blown in by secondary air fan into the furnace to burn completely as shown in Figure 3.

Figure 3: Fly Ash Re-Injection System

Combustion Air Preheater

The combustion air preheater is definitely one of heat exchanger applications. Based on Figure 1 below, flue gas simply leaves steam boiler and passes via air preheater. The combustion air is passed through this equipment too to increase its temperature before being combined with boiler fuel.

Because the temperature of combustion air is lower than the temperature of flue gas, combustion air receive heat transfer from flue gas through combustion air preheater in the process of convection heat transfer. The heat transfer make temperature of flue gas lower and consequently minimizes its heat loss and also decreases the air temperature to stack. The additional heat throughout the combustion air going into boiler furnace improves the process of combustion. This decreases the fuel need in quantity equivalent in the value of heat to quantity of heat which have been taken in the application of heat exchanger such as combustion air preheater, therefore increasing efficiency.

Through the utilization of air preheater application, about 1 % of fuel is unspent for every single 40 F go up in the temperature of combustion air.

Figure 1: Combustion Air Preheater
(Source: Book-Boiler Control System Engineering-G.F Gilman)

Mechanism of Economizer

Economizer is one of steam boiler’s equipment which is used to heat feedwater before it is supplied into steam drum. Economizer is the heat exchanger equipment to increase boiler efficiency by absorbing heat recovery of flue gases. The lower temperature of flue gas out from stack, the heat loss will be less and the fuel which is needed to convert water into steam will be also less in certain circumstances. So it can be said that economizer can save the fuel efficiently. Economizer will make temperature of feedwater higher, so steam boiler can produce steam easily.

The heating process of water in the economizer is like an heat exchanger, water is distributed inside tubes and flue gas outside tubes. The hot flue gas outside tubes flow and making contact with outside surface tube, so the heat transfer occur between hot flue gas and surface metal tubes by convection. Water inside tubes receives heat transfer from metal tubes, so temperature of water is higher than before enter economizer. Contact of flue gas flow to feedwater flow is regular and perpendicular. It is controlled and regulated by setting the flue gas flow.

Furthermore, feedwater that has been heated in economizer is sent to steam drum through connecting pipes. In the steam drum, feedwater will be boiler water and be heated again in water wall tubes to be saturated steam and superheater will make it as superheated steam.

The advantages of using economizer as initial heater are as follow:

- The metal wall of steam drum will not easy to be contracted, shrivel and broken because the incoming water is not cold condition so the cost maintenance will be smaller.

- Increase steam boiler efficiency and decrease heat loss.

- Save the fuel needed to perform combustion process

- The size of furnace can be smaller because the requirement heat surface is less than without using economizer.

Safety Valve in Superheater and Reheater

Superheater and reheater in steam boiler must be equipped with safety valve respectively. Safety valve in superheater is installed at main steam line piping between superheater outlet and the first main stop valve. Safety valve is one of appurtenances in steam boiler which is used to release pressure if the working pressure exceeds maximum allowable working pressure.

Designer steam boiler should consider the size, relieving or discharge capacity, set pressure and number of safety valve. These parameters depend on the presence of valve between steam boiler and safety valve in superheater and the pressure drop upstream of safety valve.

Installation of safety valve in reheater must be applied minimum one safety valve. Determining discharge or relieving capacity of safety valve in reheater is different with safety valve in boiler. It must be calculated separately. Safety valve in reheater can be located between reheater outlet and the first main stop valve.

If the temperature of steam flow exceeds 450 F, the safety valve should be equipped with casing with a spindle, bonnet, body and the base. These materials are fabricated from alloy steel or steel, or other material which has high heat resistance. The connection of safety valve can be flanges to make easy for maintenance or welded connection.

Figure 1: Safety Valve in Superheater

Pressure Gage in Steam Boiler

Steam boiler use pressure gage to measure pressure at some places either for water fluid or steam fluid. Pressure gauge is useful for the operator or personnel who working in steam boiler area to see working pressure and try to control the pressure under MAWP (Maximum Allowable Working Pressure). The pressure gauge is place in area which easy to see or visible for the operator. The pressure gage is different with gage pressure. The pressure gage is the equipment to measure pressure while gage pressure is the unit of pressure (usually indicated as psi = pounds per square feet) above atmospheric pressure.

Pressure gage is commonly classified as three types as the following below:

1. Bourdon pressure gage
The bourdon pressure gage is type pressure gage which has bourdon tube, it s an oval cross section of hollow tube. The tube has two ends, open and close. Open end is connected to fluids either water or steam and close end is connected to mechanical linkage in gage pointer. When the pressure builds up, the bourdon tube will be straightened out.

2. Bellow pressure gage
This type is commonly applied for the pressure under 30 psi.

3. Spiral pressure gage
The spiral pressure gage is modification design from bourdon pressure gage type. It has spiral and long pressure sensing.

Hydraulic & Mechanical Ash Handling Equipment

There are three types of ash handling system; pneumatic, hydraulic and mechanical ash handling system. Hydraulic ash handling equipment is usually used to convey bottom ash. Illustration below is sample of working principal on hydraulic ash handling equipment.

Figure 1: Hydraulic Ash handling Equipment
Source: Book - Central Boiler Plants - Headquarter Department of The Army

The hydraulic system applies high pressure water jet to take bottom ash from hopper which was located under steam boiler or under stoker. The bottom ash can be taken out from the hopper by instruments such as water jet nozzle and spray nozzle. The bottom ash is then distributed by water jet through sluice way to wet storage sump (see Figure 1).

The treatment to dispose ash is different for fly ash. Fly ash from the hoppers is disposed pneumatically by water jet exhausters then distribute to air separator to separate air from fly ash and then air will be discharged to atmosphere. The end of process, the mixture fly ash and water are conveyed to wet storage sump (see Figure 1).

Another type of ash handling system is mechanical ash handling equipment. This equipment can be employed for small scale boiler which uses stoker type. This type can be also used to convey both for fly ash and bottom ash. The system use mechanical equipments such as bucket conveyor, screw, drag to convey ash from steam boiler to container or silo or storage bin.

Pneumatic Ash Handling Equipment

There are three methods of ash handling equipments. One of them is pneumatic ash handling equipment. Pneumatic system is rarely used to transport bottom ash; it is only used for small scale boiler. Pneumatic ash handling system is often employed for carrying out fly ash.

For more detail please see figure 1 below:

Figure 1: Pneumatic Ash Handling Equipment
Source: Book - Central Boiler Plants - Headquarter Department of The Army

At the figure above explain pneumatic ash handling system with vacuum type. Vacuum pump which is driven by motor is installed into exhauster to generate vacuum pressure. Ash which had been collected by the hopper will be distributed to the pneumatic ash handling system. The exhauster generate suction to make air flow in the line pipe rapidly, so dry ash will be induced and flow to primary collector and secondary collector. The collector is completed by counter balance drop door which allow the ash put down into storage bin firmly and periodically.

The counter balance drop door is normally sealed and closed to maintain the system in the negative pressure. The system is running cycle and periodically, to open the drop door the pressure will be made similar, so the ash can drop into storage bin.

Ash Handling Equipments in Steam Boiler

Steam boiler need to manage not only about coal handling but also about ash handling. Ash is a remaining product of combustion. Ash will be many found in steam boiler which uses coal as its fuel. Steam boiler needs some places to collect ash and then remove and dispose it together in a system which is used to take care about ash.

From the place collection, ash can be classified into two types; bottom ash and fly ash. Ash which be collected in the furnace or under stoker is called bottom ash, while the ash which be collected in the other areas such as boiler bank, air heater, economizer, and multi cyclone is called fly ash. Bottom ash tends to agglomerated clinkers and hard. Fly ash is often not heavy, soft and easy flow.

Handling management for bottom ash and fly ash are to be better if performed separately. Therefore steam boiler must be equipped for bottom ash handling equipments and fly ash handling equipments respectively. Bottom ash can be re-used for treatment in winter road, etc and fly ash can be re-used to be sold again to concrete manufacturer. This condition will be great advantage on economic side for the owner.

Large scale boiler usually applies more complete ash handling equipments than small scale boiler. Ash handling equipments are generally classified into three types as the following below:

1. Mechanical ash handling equipment

2. Hydraulic ash handling equipment

3. Pneumatic ash handling equipment

Coal Handling Equipment in Steam Boiler

Steam boiler can be distinguished based on fuel classification. One of fuel types is coal. Steam boilers which use coal as its fuel for combustion certainly need equipment for coal handling. The size and capability of coal handling equipment depend on capacity / rating of boiler, amount of required fuel, storage and location area. The big storage area will be advantage when supply coal is delayed to the power plant area. Generally coal storage capability of boiler is designed for 3 months period or longer.

Some of equipments are generally used for coal handling as the following:

1. Bunker and silo

Bunker is the equipment will be made from steel with protective coating (to eliminate abrasion and corrosion) and used for coal storage in steam boiler. Bunker is connected to coal spreader to remove coal form coal bunker to the furnace. Silo is used for reserve storage and made from steel or concrete.

2. Hopper

Hopper is the equipment which use grate to filter oversized coal form truck or car then distribute coal to conveyor system or feeder.

3. Bucket elevator

Bucket elevator is the equipment for lift coal vertically. This equipment consists of bucket, twin chains and endless chain.

4. Coal weighing

Coal weighing is used to measure of weight of coal when it is received first in the hopper. Coal weighing is used to know the quality and the quantity of coal.

5. Feeder

Coal from hopper to bucket elevator is conveyed and managed by feeder.

Thermodynamics Term

Steam boiler has main task to convert water to high quality steam. When water is heated at atmospheric pressure, water will be converted to steam at temperature 212 F. When water is heated at higher pressure than atmospheric pressure, the boiling temperature will increase.

Enthalpy is the heat energy which is required to heat water from temperature 0 C (3 F) to the boiling temperature. Enthalpy is expressed as Btu/lb (British thermal unit per pound). When temperature from 32 F is increased gradually until 212 F, water will go to the boiling point temperature. If heat temperature is added more than 212 F, the water will converted to steam and the temperature can called as steam temperature.

Saturation temperature is reached when temperature of water is same with temperature of steam. Saturation temperature shows that at the boiling process, temperature is constant. Enthalpy of evaporation which means the heat required to convert water liquid phase to steam phase, will occur when heat temperature is increased from the boiling temperature.

The total enthalpy of saturated steam is the sum of enthalpy of saturated liquid and enthalpy of evaporation. Another means is total heat which is required to convert water and produce steam totally (see figure 1).

From figure 1, can be known that phase 1-2 is water phase, 2-3 is the boiling phase where there are mixture between water and steam at constant temperature. Phase 3-4 is superheated phase where water is converted 100% to steam.

In steam boiler, phases 1-2 occurs in economizer, water drum, downcomer and lower drum, while phase 2-3 occurs on top 1/3 furnace tubes and steam drum. Finally phase 3-4 occurs in superheater and reheater.

Steam Separator in Boiler

Steam separator has main function to separate water and steam and this equipment is usually located in steam drum. Water surface in steam drum is turbulent, so make it easy to mix between steam and water. The principle of steam separator is make steam flow is changed in any direction. Because of density of steam is lighter than water make steam can be distributed easier than water. The water droplet which has higher density will be separated and dropped from steam. Moisture will be removed by steam separator to eliminate damage and erosion if water or wet steam is distributed to the steam line.

There are some types of steam separator. For small scale steam boiler, steam separator consists of dry pipe which has a lot of holes at the top and two holes at the bottom half. The mixture steam-water is directed through the top half holes dry pipe, turbulent moving force the mixture to separate between water and steam. Steam will flow to steam line and water will drop through bottom holes (see figure 1).

Fig. 1: Dry Pipe Steam Separator
Source: Book - Boiler Operator's Exam Preparation Guide - Theodore B. Sauselein

For big scale boiler which has complexity equipment, steam separator method use centrifugal force for better result. The mixture steam-water is forced to move around the cyclone and make the rotation (see figure 2). The more turbulent moving force the mixture separate easily.

Fig. 2: Centrifugal Steam Separator
Source: Book - Boiler Operator's Exam Preparation Guide - Theodore B. Sauselein

The Role of Blowdown in Water Treatment

The role of blowdown is necessary to treat water in steam boiler. Blowdown is used to eliminate concentration of impurities and steam boiler should be free from scale. Amount of blowdown should be balance, do not too high and do not too low. If too high, the cost for chemical treatment and energy loss will high too, but if too low will make high concentration of impurities. There is not standard to regulate the amount of blowdown but practically it range between 1% until 25% regarding to the flow of feed water.

The flow of blowdown can be intermittent or continous flow depending on its use. In the classification of steam boiler based on tube type, there are two types of boiler, water tube steam boiler and fire tube boiler. In the water tube boiler, concentration of water in steam drum is controlled with continuous blowdown but in the mud/water drum or bottom header is controlled by intermittent to reduce possibility disruption of circulation in the steam boiler. In fire tube boiler, the flow of blowdown can be done with either intermittent or continuous. The amount, duration and frequency of blowdown can be controlled depend on requirement of water treatment, operating condition and design of steam boiler.

Classification of Superheater in Steam Boiler

Superheater is a device consists of tubes which get the heat from the product of combustion to add additional heat into steam, so the temperature of the steam passing through the tubes raise higher than its saturation temperature. The superheater can help steam boiler increase its capacity because help turbine generator get its required steam both in terms pressure and temperature.

Classification of superheater can be classified based on design of flow:

1. Parallel Flow Superheater

A superheater which has direction of steam flow in superheater same with the direction of flue gas flow

2. Counter Flow Superheater

A superheater which direction of steam flow in superheater opposite with the direction of flue gas flow

3. Mix Flow Superheater

A superheater which direction of steam flow in superheater same and opposite with the direction of flue gas flow

Classification of superheater can be classified based on heat transfer:

1. Convection Superheater

The convection superheater is located somewhere in the flue gas flow, where it absorbs heat transfer by convection.

2. Radiant Superheater

Radiant superheater is located in or near furnace of steam boiler and receives heat transfer from combustion process by radiation.

Classification of superheater can be classified based on arrangement:

1. Vertical Superheater

The superheatar are arranged vertically. This type has is easy to suspend and has free moving to expand. But the disadvantage, it is not drainable.

2. Horizontal Superheater

The superheatar are arranged horizontally. This type has is more difficult to suspend and should give special support to give moving for expand. But the advantage, it is drainable.

Design Spray Desuperheater of Steam Boiler

In steam boiler, desuperheater can be known as attemperator which has function reduce and control temperature of superheated steam. Superheated steam is derived from saturated steam which be heated again through superheater. Temperature of superheated steam must suitable for turbine generator. If temperature of superheated steam is overheated, desuperheater with type spray will sprays amount of water from steam boiler feedwater pump into steam flow to reduce its temperature.

Amount of water will be injected into superheated steam must have high purity, if not it can leave some troubles like deposit on the superheater tubes and can cause erosion on turbine blade. Design spray desuperheater type must include thermal sleve in pipe line desuperheater, to avoid thermal shock by water droplets which are sprayed through the nozzle strike the hot surface of pipe desuperheater.

Fig. 1: Design Spray Desuperheater of Steam Boiler

Air System Devices of Steam Boiler

Steam boiler needs auxiliaries and appurtenances to perform it working in good condition efficiently and safely. One of steam boiler’s auxiliaries is air system devices. Air system provide sufficient air in combustion process of steam boiler and as medium heat transfer in pressure parts like water wall tubes, superheater, generating bank, economizer, air heater, and the like.

Air system consists of devices as follow:

Force Draft (FD) Fan

FD Fan force primary air to furnace steam boiler through burners or grates at pressure above atmospheric pressure (positive pressure).

Induced Draft (ID) Fan

ID Fan produces induced draft to suck flue gas from the furnace

Secondary Air (SA) Fan

SA Fan supply air to controls combustion efficiency by supervising how completely the fuel is burned

Air Heater

Air heater is heat exchanger device to heat air from FD Fan to be supplied to furnace steam boiler to increase efficiency of combustion process

Air Compressor

Air compressor is a device to press air and as storage of air. This device is used to supply cooling air at peed door or peep hole (an opening used to observes furnace) and supply for energize instrument air.

Air Dryer and Filter

This is a device to remove water from compressed air and filter solid particulates such as dust.

Air Piping & Ducting System

Air piping and ducting system is a collection of pipes and ducts which in routing to deliver air in the steam boiler system

Stack of Steam Boiler

Fig. 1: Construction of Stack in Steam Boiler System

Stack is a equipment to take out the product of combustion at a sufficiently high elevation to prevent disturbance caused by ash, low flying smoke, and soot and to disperse the combustion gases. To perform flue gas flow through steam boiler room such as furnace, superheater, steam boiler bank, economizer, air heater, dust collector until be discharged to atmosphere, requires a certain amount of draft. Amount of draft can be generated by fan either force draft fan or induced draft fan to overcome the pressure drop (draft loss) that are developed in the steam boiler. Beside that, height and difference between the outside air and inside flue gas temperature of the stack can produce the draft.

Excessive heat temperature of stack is something should be avoided because it show that there are heat loss and efficiency reduction of steam boiler. The following formula may be used to calculate draft generated by a stack:

Stacks are designed in the worldwide steam boiler system are commonly completed with caged ladder, walk way, and instrument nozzle to measure the concentration of either excess O2 and CO2 to determine the operating excess air level. CO or carbon monoxide is also measured to determination of incomplete combustion in flue gas of steam boiler.

Classification of Soot Blower

Fig.1: Long Retractable Soot Blower

Soot blowers that are installed in steam boiler commonly can be classified as:

1. Long Retractable Soot Blower

This type of soot blower is located in area superheater and reheater. There is not temperature limitation in its use. Has a pair (2) of nozzle in lance tube located on both side in exact opposition (angle 0^o and 180^o) with diameter approximately 22 or 25 mm. The steam flow through soot blower is approximately 4 to 20 tph. Need more space to place long retractable soot blower on the sides of steam boiler.

Fig. 2: Wall Soot Blower

2. Wall / Short Retractable Soot Blower

This type of soot blower is located in area furnace. There is not temperature limitation in its use. Has 1 or 2 nozzle in lance tube with diameter approximately 25 mm. The steam flow through soot blower is approximately 3.5 tph. Mostly used in high temperature furnace of Pulverized Fuel Boiler. One soot blower is required to blow furnace area in every 10 m².

3. Rotary Soot Blower

Fig 3: Rotary Soot Blower

This type of soot blower is located in area boiler bank, economizer, and air heater. Its use is limited to temperature 1100^o C. Have many nozzles in lance tube with diameter approximately 8 mm. The steam flow through soot blower is approximately 3.5 tph. Maximum lance length is limited until 7 m, if the steam boiler larger than 7 m, so soot blower will be installed in both sides and can be operated by motor or manual.

4. Rake Soot Blower

Fig. 4: Rake Soot Blower

This type of soot blower is located in area fin tube economizer and vertical tubular air heater. Its use is limited to temperature 530^o C. Have many sets of nozzle. The steam flow through soot blower is approximately 3.5 – 4.5 tph. Dimension of rake soot blower is limited to 5 m length and 3 m width.