DE3023570A1 - Solid fuel combustion system with fluidised bed - allows fuel and absorbent to be delivered together - Google Patents

Abstract

The solid fuel combustion system is for boilers with fluidised beds, means for handling the fuel, absorbent, air, ash and fumes being included. It has an immersion heat exchanger allowing regulation from non-load to full-load, and fuel and absorbent can be delivered together. Fuel can be transported pneumatically and by pravity, being delivered mixed with the absorbent. The fluidised bed (9) in the hopper prevents their separation. A secondary air suply (36) can be provided via the lower part of the boiler and the annular gap, giving a hiqh combustion rate, while keeping the lower part of the boiler cool and free of ash.

Description

Fluidized bed combustion system

Description The combustion in the fluidized bed (also fluidized bed or fluidized bed offers a number of advantages over incineration in flight (Dust firing) and combustion in the fixed bed (grate firing).

Fluidized bed combustion in particular has some physical features and chemical benefits, including: those that lead to low-pollutant flue gas emissions and enable the use of a very wide range of fuels. The heat transfer coefficients between bed and immersed heat exchangers are very high high, resulting in small heat exchanger surfaces and high power densities.

With regard to regulation and control and automation however, special features must be taken into account, sq e. B. the limited power control range. The fluidization state of the bed is - depending on the grain size of the bed material or its grain distribution - at a minimum flow velocity of the fluidizing agent achieved. With increasing gas throughput and thus increasing gas velocity and, depending on the gas temperature, increasingly solid is discharged from the bed.

With a fixed ratio of oxygen required for combustion (Air) to oxygen (air) passed through the bed (air ratio: < = constant) is the relationship between combustion performance and fluidic fluid speed with a constant bed area. So the power control is only in a limited area by changing the combustion air volume flow possible. In systems with bed sections (multiple vortex beds), additional and Switching off individual sections, the power control range can be increased. Latter The procedure is comparable to that used in multi-boiler systems.

1) the terms are used synonymously To the Ignition of a fluidized bed is the entire bed mass at the ignition point of the fuel to warm up. Due to the intensive exchange of substances and energy, it is in a state of vortex even when heating energy is supplied to only one point on the bed from a uniform Going out of bed temperature. For reaching the fuel-dependent ignition temperature is, one assumes a bed mass that is approximately constant in all operating states from supplying a relatively large amount of external or auxiliary energy.

If a bed should also be able to be operated in the lower partial load range, is to work with intermittent operation. The bed cools down when it is stationary. The heat content of the bed including that of the bed container (sensible heat) determine the cooling behavior. Depending on the conditions, operation can be carried out after no-load operation without auxiliary energy supply can be resumed into the bed by adding oxidant and fuel (bed temperature> ignition temperature) or it must be supplied by auxiliary energy the ignition temperature can only be reached (bed temperature <ignition temperature).

The cooling of the bed or the energy flow in the no-load case is also determined by the energy flow through the immersion heat exchanger in the load case Removes heat from the bed. The immersion heat exchanger and the cooling medium take the No load trap, if at the same time the coolant medium mass flow is zero, the temperature of the bed. The state of aggregation of the cooling medium is accordingly the prevailing conditions. Becomes the hot immersion heat exchanger lying in bed when applied with relatively cold coolant when starting up, the result is considerable Thermal exposure problems.

In the case of solid fuel firing, the fuel supply requires ash removal and ash removal involves considerable effort. The present invention lies a supply and disposal concept that is more similar with just a few facilities Technology that solves supply and disposal.

The overall concept of the invention is that from the truck (7) the fuel (Fine coal, pellets, etc.) delivered and with the pneumatic one on the truck Dense phase or flight conveyor is transported into the coal bunker (2). The bunker is vented into the environment via filter (8). The bunker is in the building or stationed outside.

It has a fluidization base (9) for discharging the material and a dispensing device. With the fuel, a sulfur binder such. B.

Limestone or dolomite delivered. This sorbent is either with the fuel is mixed in a certain ratio or is in a separate one Bunker stored. The sorbent bunker (11) also has a fluidization floor (12) and an extraction metering device (13).

From the bunker (s), the solids are pneumatically transferred to the boiler (1) transported. The fan (3) supplies air for the fluidization trays (9, 12) in the bunkers (2, 11), the fuel and sorbent transport to (1), the incineration, the ash transport via the flap (14) and (15) into the ash bunker (5), the filter pounding air for the ash bunker filter (28) and, if applicable, the carbon and sorbent bunker filter (8, 16), the fluidization floor in the ash bunker (17), the control and the pneumatic drive actuated flaps and drives (the control can also be electrical or electronic be), the heating air circulation via the injector (18), the combustion air for the U1 or gas burner (19) if the heating is not electrical with an E-resistance heater (20) takes place, the lifting device (21, 53, 54) on which the invention is based, if this is not operated mechanically or hydraulically.

In the fluidized bed (22) there is an ash / lime (dolomite) / gypsum / coal mixture before.

The solid matter is fed into this with the combustion air via nozzles (23) registered. One or more further combustion air feeds (24) can be provided will. The bed (22) is operated at a combustion temperature of 800-950 ° C. Due to the submerged heat exchanger surface (30), the shift is in load operation kept at this temperature.

The flue gas from the combustion flows through the convection heating surface areas (25) and leaves the boiler with dust content. The flue gas dedusting (4) takes place via a cyclone and / or cloth or E-filter, the dust is removed via the flap (15) transported by conveying air via valve (26) into the ash bin (5). The flue gas reaches the chimney via the flap (27).

The bed deduction takes place via flap (14) to the ash bunker (5). The dedusting the ash bunker takes place via the cloth filter (28) with automatic knocking device, the clean air is fed to the chimney (6) or the fan (3).

The volume of the ash bunker is adapted to the coal bunker, whereby the ash content of the fuel, the fuel / sorbent mass ratio and the The bulk weights of the solids in the containers are important determinants. After the coal has been unloaded, the ash is placed in the ash bunker via the suction nozzle (29) (5) Loaded onto the truck by pneumatic suction conveyor installed on the truck. The fluidization base (17) causes complete discharge. Is the ash bunker Geodetically high enough, can be in connection with the fluidization floor be loaded by gravity.

In the boiler (1) the combustion takes place in the fluidized bed (22) from which The fluidized bed and energy (heat) is removed from the flue gas passages. The pressure vessel is according to the invention characterized in that the heat exchanger (30) upwards or move down or the fluidized bed container (31) can be lowered or raised can.

In the no-load case, the fluidized bed container (31) is covered by the cover (32) closed. The heat loss through radiation and convection is therefore lower, because the container and cover are heavily insulated (33). According to the invention, the cover moved and lowered with just one cylinder, with an asbestos seal on the Bed container rests. The energy content of the fluidized bed material (22) and the container (31) is so high that with the appropriate insulation (33) it can take several hours to several days Standstill is reached without bed cooling below the ignition limit. The bed can can be started up without external energy according to the no-load condition.

This also applies to beds with relatively very low performance large surface / volume ratios.

According to the invention, the nozzles (23) for the air supply are designed in such a way that that the solid / air mixture can be introduced into the bed at the bottom. they are Made of heat-resistant metal or ceramic and easy to exchange. The mounting openings (34) allow access. The two-phase mixture is possibly Divided into partial flows below the bed. Depending on the bed area, this results in a to several nozzles (23). The shape of the nozzle inserts (35) causes distribution of the emerging two-phase mixture over the nozzle circumference. So every nozzle has one corresponding area of effectiveness. The air ratio control can be through additional Combustion air supply (24) can be improved. According to the invention, the secondary air is supplied via the Valve (36) in the lower boiler area and from there, cooling the internals, for Annular gap (55) between dust guide cone (45) and container wall (31) over the fluidized bed.

The supplies to the fluidized bed floor are made, provided a lowering device of the bed container (31) is provided via flexible lines, pipelines with rotatable connections (56) or via trumpet tube (37).

The lifting drive takes place pneumatically, whereby the cylinder cross-sections are so great that the pressure of fan (3) is sufficiently high. The container (31) is provided with guide devices (38). The drive can also be mechanical or electrical or done hydraulically. Larger units require, among other things. mechanical or hydraulic Lifting devices.

The immersion heat exchanger (30) is firmly anchored in the boiler (1) if the bed can be moved vertically or if the bed is fixed in the boiler stands. The lifting device for the heat exchanger (53, 54) is pneumatic, mechanical, electrically or hydraulically driven. The coolant supply and return are flexible (40). The lifting device (53, 54) sits outside the boiler, the wall bushings are sealed with shaft tubes (41). The hub is provided by a translation in the Vertical with the lifting drive (53) or by rotating around one at immersion heat exchanger height Pivot point (54) arranged laterally outside the boiler (a few degrees of angle) achieved.

The heat exchange between the bed and the coolant takes place via the plates or tubes of the submerged immersion heat exchanger. The exchanger surfaces or tubes (43) are characterized according to the invention by the water flow in the inner and outer pipe (43) off. The individual pipes can expand freely, the same applies to the Collectors (44). For beds of great height, it may be necessary to have horizontal heat exchanger pipes (Bundle) to counteract undesirable strong bubble formation. The collectors (44) are designed so that they leave a large free cross-section above the bed, so that the flue gas can flow through unhindered.

The flue gas leaves the bed via the dust guide cone (45) in one Calming and afterburning chamber (46). Larger particles sink due to the increasing Cross-section decreasing flow velocity and that on the flue gas path over the convection heating surfaces decrease in temperature. The dust guide cone (45) prevents the sinking into the lower boiler area (48). In order to build-up on the cone avoid, the pneumatic knocker (47) is actuated.

The flue gas path leads to convection heating surfaces via the deflection areas over to the flue gas cleaning (4) and from there via the flap (27) to the chimney (6). the The arrangement of the convection heating surfaces is to be designed freely in large areas. So are ring links, row links, smoke tube arrangements, but also tube bundle heat exchangers to realize.

The arrangement can match the sections of fixed bed boilers for the heat transfer area in the temperature zones of 800/950 OC and below. The dust load of the flue gas must be taken into account in the structural design.

In stationary operation with constant bed temperature, the over the heat exchanger (32) to be withdrawn from the bed substantially by the amount of heat the following factors determine - fuel mass flow and calorific value, - energy flow through ash / sorbent removal (sensible warmth and unburned matter), - enthalpy of formation the sorbent reactions, - flue gas temperature, flue gas mass flow and composition, - Energy flow through the supply of solids and air into the bed, - Heat losses through Convection and radiation.

The heat output of the immersion heat exchanger is to be regulated by - change the immersion depth, - change in coolant mass flow, - change in coolant temperature difference.

The first-mentioned type of rule takes place via the bed or immersion heat exchanger lifting device (21, 53, 54) the latter by the controllable circulation pump (49) or the change the circulating mass ratio between the immersion heat exchanger and the flue gas convection heat exchanger or by combinations. Path size for regulating the immersion heat exchanger output is the layer temperature via the temperature sensor (50).

The combustion output is regulated via the combustion air mass flow (24, 36, 51) and the fuel mass flow (10) in the range of permissible gas velocities in the shift. The air ratio is determined by determining the mass ratios or based on the ° 2 or CO content in the flue gas, determined by the sensor (52), regulated.

The firing system can be operated without supervision, the statutory one Regulations such as operational safety, emission behavior, etc. are fulfilled. Firing systems of the concept described work with one Degree of automation comparable to oil-fired boiler systems. Are through the properties of the system according to the invention compared to the plant and operating costs other systems favorably. Under given market conditions, the concept opens up the coal or solid fuel application areas that arise from technical-economic Reasons so far could not be covered by solids control.

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Claims (25)

Fluidized bed incineration system claims to incineration solid fuels in boilers with a VJirbel layer including the fuel, Sorbent, air, ash and smoke gas transport system, characterized in that in addition to known control methods through the construction and arrangement of the immersion heat exchanger a large control range from zero load to nominal power is achieved, the Immersion heat exchanger is designed to be thermally highly resilient, the transport system is similar, the burnout is very good and the delivery of fuel and Can be sorbent together. 2 Method according to 1, characterized in that the solids transport processes in the system with air and gravity as the drive means from an air delivery device to be served. 3 claim 1, characterized in that the fuel and the Sorbent are delivered as a mixture and through the fluidization tray (9) in the Bunker (2) segregation is prevented (mass flow). 4 claim 1, characterized in that through the secondary air supply (36) over the lower boiler area (48) and the annular gap (55) high burnout achieved and the lower boiler area is cooled and kept free of ash. 5 claim 1, characterized in that the power control for all load conditions through the start-up control, no-load control and load control is made possible. 6 claim 5, characterized in that the change in the combustion performance (Load control) by changing the solids / air mass flow into the bed (22) takes place via the devices (10, 13, 24, 36, 51, 58). 7 claim 5, characterized in that in no-load operation the on / off regulation the immersion heat exchanger (30) is removed from the fluidized bed (22). 8 claim 5, characterized in that in the start-up the heating by Ul / gas heating burner (19) or via an electric resistance heater (20), their work by the start-up air circulation via the flap (58) and the warm-up air injection (18) is kept low. 9 to claim 6, characterized in that the regulation of the Fluidized bed through the immersion heat exchanger (30) dissipated heat the immersion depth of the immersion heat exchanger (30) takes place. 10 claim 6, characterized in that the thermal output of the immersion heat exchanger via the change in the coolant mass flow and / or the coolant temperature difference he follows. 11 to claim 10, characterized in that the coolant mass flow change through the immersion heat exchanger (30) via the pressure difference influencing device (49) takes place. 12 claim 5-11, characterized in that the layer temperature the fluidized bed (22) is detected via the temperature sensor (50) and the bed temperature is kept in the range of 800 - 950 ° C during load operation. 13 Claim 1, 5, 7, characterized in that the layer (22) with the layer container (31) lowered or raised by the lifting device (21) can be, the heat exchanger (30) is fixedly anchored in the boiler. 14 claim 1, 5, 7, characterized in that the immersion heat exchanger (30) pulled out of the layer (22) or into the Layer can be lowered, the layer and the layer container are stationary, the wall ducts are sealed with a corrugated tube (41). 15 claim 1, 5, 7, characterized in that the immersion heat exchanger (30) pulled out of the layer by the lifting device (54) by means of a rotary movement or is lowered into the layer, the layer and the layer container are stationary, the wall duct is made with a corrugated pipe (41). 16 claim 1, 5, 7, characterized in that the fluidized bed container (31) in the zero case, if the immersion heat exchanger is not in the shift, is closed with the insulated cover with drive (32). 17 to claim 16, characterized in that the drive for the cover pneumatically or hydraulically via just one cylinder, which is outside the lower boiler room (48). 18 claim 1, 2, 5, 6, characterized in that the air and Fuel / sorbent mass flow and their relationship to one another in the load control range can be determined by the devices (10, 13, 18, 24, 36, 50, 51, 52, 57, 58). 19 claim 1, 7, 13-15, characterized in that the immersion heat exchanger (30) with double tubes (43) with low immersion resistance and very high heat resistance and variable load capacity is equipped. 20 Claim 1, 4, 5, characterized in that the dust guide cone (45) is provided with a knocker (47). 21 Claim 1, 2, 7, 13, characterized in that the solids / air mixture supply, the air is supplied into and the ash is removed from the layer via trumpet pipes (37). 22 Claim 1, 2, 7, 13, characterized in that the solids / air mixture feed and the air is supplied to the layer via flexible lines. 23 Claim 1, 2, 7, 13, characterized in that the lines for the solids / air mixture supply and the air supply via a line with angle tracking takes place via three pivot points (56). 24 claim 1, 4, 5, characterized in that when starting off the no-load operation before the supply of vortex air with secondary air (36) the afterburning and boiler room is flushed. 25 claims 1, 4, 5, 18, 24, characterized in that over the Starting air recirculation injector (18) and flap (58) in the load control case, flue gas is returned can be and thus the load control range is increased.