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WASTE HEAT RECOVERY BOILER

    WHR Boilers behind DRI kilns. AEI has WHR Boilers of capacities 5, 10, 38 & 52 TPH suitable for 50,100, 350 and 500 tpd DRI Kiln exhaust gases pressure upto 110 kg/cm2 SH temp 525oC. WHRB can also be supplied for Steel Plant kiln , blast furnace gas, Coke oven gas, Cement kiln gas etc.,

    GENERAL DESCRIPTION OF WHR BOILER

  • Water tube Waste Heat Recovery system containing evaporators, super heaters, economizers, associated system and interconnecting piping, inlet and outlet ducts, expansion joints, ladders and platforms, etc. The system components are made in modular sections and each module is fully assembled in the shop. The evaporator, super heater, economizer and the inlet transition duct are shipped as individual modules.
  • The system has been specifically designed to meet the requirements of customer as per the Waste Heat released from the system. All the pressure parts are manufactured in strict accordance with the requirements of IBR and stamped accordingly.

    • WATER AND STEAM CIRCUIT

  • The deaerator water is stored in the deaerator storage tank. The deaerated water at 126’C is fed to the boiler feed pump where it is pressurized to required boiler pressure. The feed water from feed pump passes through economizers and fed to steam drum. From steam drum the hot water enters into the water wall bottom header and evaporator through down comers and further heated up. The steam water mixture then rises through the water wall panel tubes and enters into the steam drum through riser tubes.
  • From steam drum the saturated steam then enters into the convection super heater. This super heated steam enters the radiant super heater, where it is further super heated.
  • This super heated outlet temperature is controlled by a de-super heater provided in between convection super heater and radiant super heater. The steam is taken to turbine from radiant super heater outlet link.

    • STEAM DRUM

  • The steam drum is of fusion welded type, liberally sized and fitted with high efficiency internals. The steam drum provided with 2 no’s manhole door to open inwards. The following nozzles in the steam drum.

    • WATERWALL

  • The water wall, walls and roofs are formed by the tubes rising from the bottom ring headers. The water wall is made of fin welded tube panels. The front water wall consists of tubes that rise from the bottom header and end in the front water wall top headers.
  • The rear wall panels is formed by the tube that originate from the rear portion of the bottom header and riser up to the baffle top header and the baffle tubes end in the baffle top headers.
  • Entire water wall is supported from the header bottom support. From the side water wall top headers there are eight riser pipes, from each header, the baffle top header they are two riser pipes, the front wall top header they are two riser pipes, evaporator-I&II outlet header there are two riser pipes, from each header to carry the steam water mixing to the drum. To protect the boiler from the effect of explosions buck stays are used. They are nothing but beams attached to channels welded to the water wall tubes.
  • The channels form a continuous beam around the wall. The buck stay beams are attached to channels with slip connections.
  • Water wall serve two functions mainly. They form a gas tight enclosure to contain the hot flue gases. They form the evaporator circuit which generates steam. Natural circulation is established by the density difference between the water in down comers and water – steam mixing in water wall. The rate of circulation adjusts itself until equilibrium is reached such that the difference between the hydrostatic head at the feet of down comers and the water wall equal to the sum of the pressure drops due to friction and acceleration of the flow medium in the circuit. Circulation will be high at lower pressure and at lower loads.
  • Circulation will be reduced when feed water temperature increases and when drum level is low.

    • WATER TUBE EVAPORATOR MODULE

  • The evaporator module is located between the super heater and economizer modules. Boiler water is conveyed from the bottom of the steam drum to water wall bottom header and evaporators module through the down comer pipes. The steam drum distributes water to the tubes and the heated water and steam mixture rises in the tubes rise back to the steam drum. The down comer and riser piping is sized to provide a natural circulation ratio greater then a 15:1.
  • The steam drum internals include distribution piping for feed water, chemical feed and continuous blow down. Each head of the steam drum has one 410mm man way for access to the inside of the drum for inspection and maintenance of the internals. The steam drum has nozzles for connecting the safety valves, pressure gage, vent valve, water columns, level transmitter, chemical feed, continuous blow down, intermediate blow down etc.

    • ECONOMIZER MODULE

  • The economizer is an inline bare tube, forced flow type, with vertical gas flow. The longitudinal and transverse spacing are maintained by two tube supports located in the gas stream.
  • The purpose of economiser is to preheat the boiler feed water before it enters the steam drum and to recover some heat from the flue gas leaving the boiler.
  • The inlet and outlet headers are positioned horizontally. It is fed with feed water by a pipe from the feed water control station.
  • The economizer coils are horizontally arranged and are split into two banks with a specific gap in between them for both Economiser-I & Economiser-II.
  • The economiser coils are suspended from the economiser casing top frame through lugs and pins. There is a link connecting the economiser outlet header to the drum.
  • he feed water flow is downward through the economizer-I & the economizer-I outlet is upward through in the economizer-II, that is, in forced flow to the hot flue gases. Most efficient heat transfer is hereby accomplished.

    • SUPERHEATER MODULE

  • The super heater module is located between the Radiant chamber and the evaporator. The super heater is a horizontal type and is designed to be fully drainable, with steam flow arranged in counter flow direction with the flue gas. The super heater tubes are arranged in two sections, one before and other after the “desuperheater”.
  • Saturated steam from the steam drum enters the super heater first stage inlet header. To enable draining of the tubes, a bottom header with 1” drain line has been provided.
  • The construction detail of the second stage super heater, located after the desuperheater, is similar to the first stage, however, to withstand higher gas temperatures. Alloy steel materials are provided the super heater outlet header has welded nozzles to install one vent valve.
  • The super heater outlet headers and tubes are supported from the water wall enclosures.
  • The super heater steam temperature is controlled and maintained around 540±5°C by injecting feed water from the desuperheater which is located behind primary super heater outlet nozzle.

    • DE-SUPERHEATER

  • Desuperheater is provided in the link connecting the primary super heater outlet header and radiant super heater inlet header. This is used to maintain the steam temperature at design value.
  • Temperature reduction is accomplished by injecting spray water into the path of the steam, through nozzles at the entering end of the Desuperheater. The spray water is drawn from the feed pump discharge line but before the feed control station. It is essential that the spray water be chemically pure and free of suspended and dissolved solids.

    • DOSING SYSTEM

    HP DOSING:

  • In HP dosing system, trisodium phosphate is dosed to steam drum to precipitate the dissolved salts forming hardness, these precipitated sludge is removed through blow down.
  • To ensure proper dosing of phosphate recommended amount of residual phosphate to be maintained can be obtained from phosphate curve which depends on the PH value of boiler water.