CN1120144A - Reheater protection in a circulating fluidized bed steam generator - Google Patents

Abstract

In cyclic fluidized bed combustion system, the final reheater that is positioned in heat exchanger of fluidized bed, heated after power cut or turbine's breaker opening but not cooled is cooled by partial steam coming from overheat and flowing through a high dropping valve. A valve at downstream of final reheater is opened for passing the fluid.

Description

The protection of reheater in the circulating fluidized bed steam generator

The present invention relates to the circulating fluidized bed combustion system under non-normal condition, when promptly flowing to the fluid interruption of reheater, protect a kind of method on the reheater surface of this system.

Why favourable fluidized bed combustion is, and many reasons are arranged.Its outstanding characteristics are to need not to use the flue gas scrubbing tower just can use high-sulfur combustor under the condition that environmental protection is allowed.In fluidized beds combustion burning process, most of sulphur contained in the fuel is removed by the adsorbent in the fluid bed (normally lime stone).In this process, because the temperature of combustion reaction is low, thereby the nitrogen oxide that produces is few.

One of them type of fluidized bed combustion is circulating fluid bed system.In this system, the air velocity in the stove is 3 to 4 times of general bubbling fluidization bed system.Small solids are brought to top, gaseous state/solid mixt that the density that grows on trees in the whole stove is lower by the fluidisation stove.Since the speed of solid by stove than gas slowly many, thereby the time of staying of solid in stove is long especially.The time of staying is long, and it is little to add granularity, makes efficiency of combustion and remove sulfur content all high, reduces the inlet amount of the lime stone of absorption usefulness simultaneously.

In the circulating fluidized bed combustion system, the solid of taking out of from stove is separated from gas by cyclone separator.The solid of discharging from the cyclone separator lower curtate passes through hermetically sealed can or siphon seal groove.In some designs, a part of solid can be guided to fluidized bed exchanger, and remaining solid later reinjects in the stove.The heat that extracts from the solid of fluidized bed exchanger can be used for further evaporating, superheated and/or again the heating.

For preventing at the excessive moisture of low-pressure steam turbine formation at different levels, the common practice is to interrupt expansion process, removes steam, is used for heating in constant voltage again, and it is at different levels then it to be sent back to low pressure turbine.This is called thermal cycle again.In circulating fluid bed system, this again thermal process be at stove convection channel, in fluidized bed exchanger or both combine under the situation of use and carry out.When using the recuperation of heat fluidized system to heat again, no matter be to use heating more separately or be used in combination with heating again in the convection channel, when upset condition occurring, when for example power failure or turbine trip, will go wrong, at this moment the fluid that flows to reheater interrupts, and the reheater surface continues to be exposed among the thermal source.

The objective of the invention is provides fluidisation stream to the reheater in the fluidized bed exchanger of circulating fluid bed and combustion system when normal fluid stream interrupts.More particularly, thus the present invention relates to after the superheater in the end, have a power failure or the turbine tripping operation make when the normal fluidisation stream of reheater is interrupted from the vapor stream changed course of Trunk Line, provide fluidisation stream to reheater.

Accompanying drawing shows the whole circulation formula fluidized bed combustion syste that reheater protection system of the present invention is housed.

Referring to accompanying drawing. There is shown take fluid bed furnace 12 to main typical recycling formula fluidized bed combustion The burning system. Coal and lime stone add the stove from hopper 14 and 16 respectively. One time fluidization air is logical Enter in the plenum chamber of furnace bottom 18, secondary combustion air passes into from 20. Stove 12 bottoms are covered with fire-resistant Brick protects it to avoid corroding and corrosion. The upper part of stove 12 has the water-cooled ancient piece of jade, round, flat and with a hole in its centre that can evaporate. Water-cooled The steam that wall produces passes in the vapor can 24 through pipeline 22, and water is fed to water-cooling wall through pipeline 26 simultaneously On.

From flue gas, separate cyclone separator 28 in company with the solid that flue gas is taken away simultaneously from stove 12.Solid is discharged from the cyclone separator bottom, handles by way of the present invention, and this is about to explanation after a while.Flue gas comes out from the top of cyclone separator 28, enters raceway groove 30, and by convection part 32.Then, flue gas generally is to handle in dust arrester, and is used to heat the combustion air before the feeding flue that is input into.

Saturated vapor leaves jar 24, enters in cold raceway groove 30 of vapour and the convection part 32, and feeds and by first convection tube row 34, enter second convection tube then and arrange 35 (in some designed, these were last superheaters).Then, steam enters and carries out overheatedly at last in the fluidized bed exchanger 50, enters in the high pressure turbine by pipeline 51 then.The discharge material 38 of high pressure turbine 36 leads to the initially hot again part 40 in the convection part 32, and steam is through part heating more there.Steam comes out from hot part 40 again, delivers to the hot more at last part 42 in the fluidized bed exchanger 44, and this is about to explanation after a while.At this moment deliver in the low pressure turbine 46 through the steam that heat is again crossed.The discharge material 48 of low pressure turbine 46 is sent boiler back to by heating by the exhaust gases part (not shown) usually.

A hermetically sealed can or siphon seal groove 52 are arranged at the bottom of cyclone separator 28, and this is an on-mechanical valve, and its effect is to head on furnace pressure the solid of collecting in the cyclone separator is sent back in the stove 12.Solid flows to entrance side downwards, flows upward to outlet side, returns in the stove in raceway groove 54 then.The base section of sealing jar is in fluidized state usually, and the material in the hermetically sealed can is arranged on each limit by different levels.The difference of level is corresponding to the pressure differential at hermetically sealed can two ends.Thereby the solid that enters entrance side is substituted in the solid that outlet side flows out.

There is a solid extraction tube 56 lower part of hermetically sealed can 52, and efflux of solids control valve 58 is housed on the pipe.This valve is called plug valve under individual cases, be used for regulating the flow of solid.This valve 58 is used for controlling the heat of fluidisation bed heat exchanger 44 outside hermetically sealed can 52 extracts, introduces, thereby regulates the temperature of reheated steam.

Fluidized bed exchanger 44 is bubble type fluidized bed exchangers, is made up of with the separated cell of weir plate some, and the dipping that is called last hot again part 42 of being equipped with in each cell is restrained and last superheater 50.Hot solids enters recuperation of heat fluidized system 44 by raceway groove 56, fluidisation in raceway groove 56, and with heat traditional hot traffic device surface 42 and 50.Originally solid enters solid distributor chamber 64, slowly leads to another cell from a cell then, returns in the stove 12 by outlet 66 again.The fluidization air that the recuperation of heat fluidized system is used provides by pipeline 68, and feeds in each cell.

When power failure or turbine tripping operation, the material flow such as fuel, lime stone and air that feed stove 12 are interrupted.The current that supply water may continue and also may interrupt, and by the water-cooling wall circulation, superheater then continues operation under the situation of decompression.Though the fluidisation stream by major loop (water-cooling wall, superheater etc.) is continuing, fluidisation stream flows out from high pressure turbine and by reheater part 40 and last reheater 42 never again.Do not cover the whole surface of reheater in the fluidized bed exchanger owing to be in the solid of unfluidized state, thereby the pipeline that is embedded in the solid is different with the speed that expands with not embedding its friendship heat of pipeline.The present invention provides fluidisation stream by last reheater 42 when the materials flow of normal reboiler circuit is interrupted, prevent reheater metal nonuniform heating.

Owing to still have fluidisation stream to flow through major loop after tripping operation or the power failure, thereby the exit of last superheater 50 continues that fluid source is arranged in (steam or water).Therefore, the pipeline 70 of band valve 72 links up the outlet line 51 of last superheater 50 and the inlet of last reheater 42.Valve 72 is electrically operated valves, under normal circumstances closes, and designs to such an extent that it is opened when having a power failure.This valve has very high pressure and falls, so it is when opening, and drops to about 700 pounds/square inch gauge and 930 from the high steam of the about 2270 pounds/square inch gauge of superheater and 1005.These temperature and pressures only are for example, rather than limitation of the present invention.Pipeline 70 and valve 72 be design make its sub-fraction be enough to cool off reheater with superheater steam offer reheater.For example from the steam of superheater outflow, about 7% to 10% just is enough to deal with problems, but this depends on the specific design of each fluidized bed plant and decides.

In order to make this steam by last reheater changed course have suitable flow, in the end reheater 42 downstreams have disposed a blast pipe or discharge line 74 and valve 76.Valve 76 is the same with valve 72, designs to such an extent that it is under normal circumstances closed, and have a power failure or during the turbine tripping operation and valve 72 open simultaneously.Valve 76 1 is opened, and steam just can be by last reheater free flow.Steam can be removed the heat of last reheater, and it is all even in permissible range to assist to keep the pipeline heat expansion, just can safe step-down but also make boiler need not electric power.

Claims (4)

1. a kind of method of operating of circulating fluidized bed combustion system, there are a superheater loop and a reboiler circuit in this system, after wherein from flue gas, separating from the fluidized solid of fluid bed furnace, minimum a part of separated solid is sent into the outer fluidisation bed heat exchanger of a minimum part that includes described reboiler circuit, described method of operating is characterised in that it comprises the following steps:

A. determine to make the condition of the normal reheater fluid stream termination of flowing through the described part of described reboiler circuit;

B. open a valve according to described definite condition, and will send the described part of described reboiler circuit to from the fluid in described superheater loop;

C. open an air bleeding valve of the described portion downstream of described reboiler circuit, make fluid stream can by and cool off the described part of described reboiler circuit.

2. the method for claim 1 is characterized in that, described fluid is a steam.

3. method as claimed in claim 2 is characterized in that, the first step-down before entering the described part of described reboiler circuit of the described steam in described superheater loop.

4. method as claimed in claim 3 is characterized in that described pressure reduces pressure in described valve.