Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22G—SUPERHEATING OF STEAM
  • F22G5/00—Controlling superheat temperature
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
  • F22B31/00—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus
  • F22B31/0007—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus with combustion in a fluidized bed
  • F22B31/0084—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus with combustion in a fluidized bed with recirculation of separated solids or with cooling of the bed particles outside the combustion bed

Definitions

• steam temperatures may be more than 300°F below the design level, necessitating extended periods for cooling the turbine before shut-down or load reduction, and for reheating the turbine before reloading. This is costly in terms of reduced efficiency, steam dumping and possible thermal cycling damage.
• the present invention provides a novel ap ⁇ proach to the design of a steam boiler in which the final steam temperature may be matched to the turbine over the whole load range, including hot and warm starts.
• I is also an object to provide reheated steam at constant or controlled temperature as re ⁇ quired by a steam turbine with single or multiple reheat stages operating with variable load and during start-up and shut-down operations.
• the in ⁇ vention is a method of operating a combustor and controlling the relative amount of heat provided from the combustor to a steam generator, steam superheater and steam reheater such that the superheated steam temperature can be controlled to a desired level independent of the steam flow rate.
• the method com ⁇ prises generating heat from the combustion of fuel in an entrained bed combustor of the type having a rel- atively fine particle fraction entrained in a fluid- izing gas, transferring the heat of combustion to the fine entrained bed particles, providing independent flow paths for the fine particles through the steam generator, steam superheater and steam reheater such
• the inventive method preferably comprises recycling the fine entrained bed particles in the desired proportion through the heat exchange compo ⁇ nents and back into the combustor to be reheated and
• the method preferably further comprises the use of a combustor of the multisolid fluidized bed type having, in addition to the entrained bed parti ⁇ cles, a dense fluidized bed of relatively coarse
• a preselected portion of the fine entrained bed particles may bypass all of the
• preselected portions may be recycled through two or all three of the components, for example, through both the steam generator and the superheater, while a second pre ⁇ selected portion is recycled only through one of the
• the par ⁇ allel controlled flow paths through the heat exchange components is the feature of the present invention which allows the operator to match the steam require ⁇ ments in terms of volume and temperature (also pres-
• the present invention is particularly adapted to use in steam turbines for power generation.
• Gases from the combustor are separated from the fine entrained particles prior to the latters entry into the heat exchange components. These gases may therefore be conventionally used in an economizer or other convective heat transfer devices of the system.
• Figure 1 is a schematic diagram of a prior art, conventional steam generator used in the electric power industry.
• Figure 2 is a schematic diagram of the present inventive steam generation system used in practising the novel method.
• __ Figure 3 is a graph comparing the effect of the load factor on the steam temperature for the prior art generator and the present invention.
• Figure 4 is a series of graphs showing the conditions present in an idealized shut-down and start up which may be closely followed according to the invention.
• water tube boilers are used to supply superheated steair. to turbines which in turn run the power generators.
• water is passed through heat exchange tubing 5 forming the internal walls of the boiler 1 and is vaporized by the heat from the boiler burners 6. Radiant heating from the proximate flame is the primary mechanism of heat transfer.
• OMPI superheater 2 is an extensive serpentine heat ex ⁇ changer which is heated primarily by convection from the hot gases generated by combustion in the boiler.
• the purpose of the superheater is of course to bring the temperature of the steam up to the level demanded by the turbine. Water is typically injected into the superheater at controlled rates to ensure that the steam temperature does not exceed the safe upper limit dictated by material properties.
• a reheater 3, which is a tubular heat exchanger located near the super ⁇ heater, has a similar purpose in reheating steam exhausted from the high pressure turbine 4 before the steam is further expanded in the low pressure turbine 7. Exhausted steam from the low pressure turbine is also sent to the condensor 8 for recycle.
• the above apparatus Whenever the turbine is running at its rated load, the above apparatus is capable of providing adequate steam at closely controlled conditions, typ ⁇ ically on the order of 1000°F and 2400 psi. In fact, the above apparatus is conveniently used when the turbine is loaded above about 70% of its rated capac ⁇ ity.
• the boiler is usually designed to generate steam at the desired conditions at about 70% of rated capacity and the tendency for steam temperature to rise at higher loads is countered by injecting water into the superheater.
• This prac ⁇ tice is commonly referred to as desuperheating.
• the boiler may be designed to superheat the steam to 1000°F at 70% load, which would result in a steam temperature at full load of 1100°F unless desuperheat control were used to lower the temperature. Therefore, at about 70% load and higher, this design would produce steam temperatures of the desired 1000°F but, unfortunately, at less than about 70% the steam temperature would be below 1000°F.
• the present invention utilizes an en ⁇ trained bed combustor with external heat exchange components which are arranged in parallel relation ⁇ ship.
• An entrained bed combustor is a "fluidized" bed in which relatively fine particles are entrained in the fluidizing gas, fuel is burned in a lower region thereof, and heat from the combustion of the fuel is transferred to the entrained particles passing th ⁇ rough the combustion region.
• the entrained fine particles are transported out of the combustor by the fluidizing gas and are captured in a cyclone to be thereafter directed in preselected qua- ntities to the heat exchange components.
• the sep ⁇ arated gases are used in convective heat transfer sections such as in an economizer.
• the fine particles are recycled through the heat exchange components in the desired relative amounts and back into the combustor to be reheated and recirculated.
• the entrained bed combustor is preferably a multisolid fluidized bed apparatus which is designed
• the operation of a multi ⁇ solid fluidized bed comprises forming the entrained bed in a first space region containing the relatively, fine solid bed particle component, forming in a more limited space region within the first region a dense fluidized bed containing a relatively larger solid bed particle component essentially comprising a material having long-term physical and chemical stability in the fluidized bed system so as to be substantially non-agglomerating and not subject to substantial at-' trition therein, providing a recirculation path such as through a cyclone separator and particle reservoir for the fine particle component from the first space region through the dense fluidized bed in the more limited space region, and operating the fluidized bed system at a velocity such that the larger component particles are effectively retained in the dense flu ⁇ idized bed in the more limited space region, whereas the fine component particles recirculate and inter- penetrate there
• FIG. 2 is a schematic drawing of the system employed in practising the invention. Operation of the entrained bed combustor in a single particle mode is similar excepting the contribution of the dense fluidized bed.
• the combustor 10 is a multisolid fluidized bed such as described in the above mentioned U.S. Patent
• a relatively large particle component is fluidized in a dense bed 12 by a fluidizing gas 14 through distributor plate 27.
• the dense bed region is contained within the larger entrained bed 11 in which relatively fine particles are temporarily retained.
• the fine particles are entrained in the fluidizing gas 14 and are eventually removed out the top of the combustor and captured in cyclone 15.
• the fine parti ⁇ cles are then recycled back to the dense bed of the combustor through the steam generator 17, steam su ⁇ perheater 18, steam reheater 19 or bypass line 30 via recycle leg 21.
• the hot fine particles of course give up heat to the water through the heat exchange tubing and convert it to steam. Heat" transfer from the fine particles in contact with the heat exchange tubing by controlled injection of flu ⁇ idizing gas entering at 31.
• the steam from the steam generator 17 then passes to the superheater where its temperature and pressure are raised and then proceeds through line 23 to the high pressure steam turbine 25.
• Heat for superheating again comes from the hot entrained par ⁇ ticles which are passed through the superheater 18 in contact with the heat exchange tubing and out through line 28 to recycle leg 21.
• Exhausted steam from the high pressure tur ⁇ bine 25 may also be reheated in the same manner if returned through line 22 to the reheater 19. Hot entrained particles are metered through the reheater at a preselected rate and the particles give up heat to the steam before the particles exit through line 29 to recycle leg 21 and the reheated steam passes back to the low pressure steam turbine 32 via line 24 where it is further expanded.
• a bypass line 30 may also be used to recycle fine particles without passing through any of the heat exchange components.
• this ideal operating situation can be achieved on a conventional water tube boiler unit only by firing the boiler at a rate which does not match the power demand, to the detriment of the boiler.
• the present novel method using the multisolid fluidized bed allows the required steam conditions and load to be met independently by manipulating the hot fine particle circulation rate and the firing rate.
• the firing rate falls faster than the load to allow the heat transfer (fine entrained particle) bed temperature to fall, so that heat transfer to the steam is reduced in line with the temperature requirement.
• the balance between the rate of steam generation and the steam temperature is maintained by careful selection of the relative flow of the fine particles in the steam generator, super ⁇ heater and reheater.
• the firing rate has only to make up the difference between total heat demand and that supplied by the fine particles on cooling.
• the firing rate is increased to raise steam pressure, supplying heat for superheat only when re ⁇ quired, by diverting hot fine particles to the appro ⁇ priate heat exchange components.
• firing rate temporarily exceeds the heat demand from the turbine, the excess heat going to heat the fine particle inventory.
• the firing rate can be matched to the boiler output.
• the present method allows much quicker start-ups over the prior boiler since the firing rate may be increased quickly without risk of overheating the superheater or reheater.
• the heat is then applied selectively to the heat exchange com ⁇ ponents or the fine particles may bypass the heat exchange components and be recycled directly back to the combustor to raise the temperature of the fine particle inventory.
• the firing rate must be slowly increased upon start-up until steam is produced and passed through the super ⁇ heater and reheater. Until then, the tubing can be thermally damaged by high gas temperatures.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Control Of Steam Boilers And Waste-Gas Boilers (AREA)
• Control Of Turbines (AREA)
• Engine Equipment That Uses Special Cycles (AREA)
• Control Of Temperature (AREA)
• General Preparation And Processing Of Foods (AREA)
• Devices For Medical Bathing And Washing (AREA)
• Fluidized-Bed Combustion And Resonant Combustion (AREA)
• General Induction Heating (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=22348374

Family Applications (1)

Country Status (14)

Cited By (1)

Families Citing this family (27)

Citations (4)

Family Cites Families (7)

• 1980
  • 1980-01-18 US US06/113,246 patent/US4312301A/en not_active Expired - Lifetime
• 1981
  • 1981-01-12 AU AU67882/81A patent/AU536859B2/en not_active Ceased
  • 1981-01-12 WO PCT/US1981/000034 patent/WO1981001970A1/en unknown
  • 1981-01-12 JP JP56500868A patent/JPH0217761B2/ja not_active Expired - Lifetime
  • 1981-01-16 EP EP81810012A patent/EP0033713B1/en not_active Expired
  • 1981-01-16 CA CA000368679A patent/CA1141972A/en not_active Expired
  • 1981-01-16 DE DE8181810012T patent/DE3166880D1/de not_active Expired
  • 1981-01-16 AT AT81810012T patent/ATE10133T1/de not_active IP Right Cessation
  • 1981-01-19 ZA ZA00810350A patent/ZA81350B/xx unknown
  • 1981-01-19 BR BR8100279A patent/BR8100279A/pt unknown
  • 1981-01-19 MX MX185614A patent/MX153043A/es unknown
  • 1981-01-31 IN IN109/CAL/81A patent/IN154038B/en unknown
  • 1981-09-16 DK DK412381A patent/DK153769C/da not_active IP Right Cessation
  • 1981-09-17 NO NO813166A patent/NO152309C/no unknown

Patent Citations (4)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events