WO2010006353A2

WO2010006353A2 - Process and device for providing a constant product gas rate from a fluidized bed gas generation plant

Info

Publication number: WO2010006353A2
Application number: PCT/AT2009/000279
Authority: WO
Inventors: Tobias PRÖLL; Hermann Hofbauer
Original assignee: Technische Universität Wien
Priority date: 2008-07-16
Filing date: 2009-07-16
Publication date: 2010-01-21
Also published as: AT507175B1; AT507175A1; WO2010006353A3

Abstract

A process is described for providing a constant product gas rate from a fluidized bed gas generation plant, comprising a fluidized bed system which is coupled via at least one circulating bed material stream (5) and comprising at least one gas generation reactor (2) having a meterable fuel feed (1, 20) and at least one combustion reactor (4), a gas conditioning stage (8) arranged in the product gas stream (7) coming from the gas generation reactor (2) and an attached gas utilization stage (9) having upstream product gas compressor (19), and also a partial recycling (13) of product gas for controlling the temperature in the fluidized bed system, characterized in that the fluctuations of the product gas rate produced originating from the fuel feed and fuel quality are compensated for by a rapidly reacting variable product gas recycling (13) to the combustion reactor (4). In addition, a device is described for carrying out this process.

Description

A method and apparatus for providing a constant volume of product from a fluidized bed gasification plant

The present invention relates to a method for providing a constant amount of product gas from a fluidized bed gasification plant comprising a fluidized bed system coupled to at least one gas generating reactor having a metered fuel feed and at least one combustion reactor, gas conditioning disposed in the product gas flow from the gas generating reactor, and a Connected gas use with upstream product gas compressor, and a partial recycling of product gas to control the temperature in the fluidized bed system and an apparatus for performing this method.

The inventive method provides a novel use of the thermal capacity of a fluidized bed reactor to dampen volume and pressure variations of a gas stream in a fluidized bed gasification plant for biomass, coal or other carbonaceous fuels in which heat is supplied via circulating bed material.

Fluidized bed gas generators of the type mentioned are known per se, for example from AT 405,937 Bl or from various publications, such as Hofbauer, H., Stoiber, H., Veronica, G., 1995, Gasification of organic material in a novel fluidized bed System, In: The Society of Chemical Engineers, Japan (ed.): Proc. Is SCEJ Symposium on Fluidization, Tokyo, 1995, Self-Publishing, pp. 291-299; Hofbauer, H. (2007). Conversion technologies: Gasification overview, in: Proceedings of the 15th European Biomass Conference & Exhibition, Berlin, Germany, pages 5-10; Hofbauer, H., Veronik, G., Fleck, T., Rauch, R., (1997). The FICFB gasification process, in: Bridgewater, AV & Boocock, D. (Eds.), Developments in thermochemical biomass conversion, vol. 2. Blackie Academic & Professional, Glasgow, UK, pp. 1016-1025; Hofbauer, H., Rauch, R., Löffler, G., Kaiser, S., Fercher, E., Tremmel, H., (2002). Six years experience with the FICFB gasification process, in: PaIz, W., Spitzer, J., Maniatis, K., Kwant, K., Helm, P., & Grassi, A. (Eds.), Twelfth European Biomass Conference. ETA, Florence, Italy, pages 982-985; Löffler, G., Kaiser, S., Bosch, K., Hofbauer, H., (2003). Hydrodynamics of a dual fluidized-bed gasifier - Part I: Simulation of a risk with gas injection and diffuser. Chem. Eng. Sci., 58, pp. 4197-4213, or Kaiser, S., Löffler, G., Bosch, K., Hofbauer, H., (2003). Hydrodynamics of a dual fluidized bed gasifier. Part II: Simulation of solid circulation rate, pressure loop and stability. Chem. Eng. Sci., 58, pp. 4215-4223.

For better understanding and comparison with the present invention, the hitherto known prior art is shown in FIG.

Referring to FIG. 1, fuel 1 is introduced into a gas generating reactor 2 which is fluidized with steam or recirculated product gas via an inlet 3. The necessary heat is supplied to the gas generating reactor by burning unreacted fuel in the combustion reactor 4 via circulating bed material 5. The combustion reactor is fluidized with oxygen-containing gas (e.g., air) via an inlet 6. The unreacted fuel is thereby transported with the circulating bed material 5 from the gas generating reactor to the combustion reactor, heat is thereby transported by the hot bed material flow from the combustion reactor to the gas generating reactor.

The product gas 7 formed in the gas generating reactor is conditioned in one or more stages 8 (eg by cooling, dust separation, tar separation, compression, etc.) and then fed to a gas utilization unit 9, which converts the product gas either into the desired final energy or to the desired material products , The exhaust gas of the gas utilization unit goes into a chimney 10.

The exhaust gas 11 of the combustion reactor 4 is also conditioned (e.g., at 12, for example, for heat recovery, cooling, dust removal, etc.) and then directed to the chimney 10. It is known that an adjustable partial flow 13 of the conditioned product gas is returned to the combustion reactor 4 in order to be able to adjust the operating temperature of the gas generation independently of the fluctuating fuel properties.

The amount and properties of the fuel supplied can not be kept exactly constant while the For many applications, the amount of product gas must be constant and constant. This is particularly the case with the direct use of the product gas in gas engines or gas turbines, which machines are running on a given constant speed load. Even when the product gas is used in industrial synthesis processes, a constant synthesis gas stream is desirable or required.

It is further known that the fluctuations in the gas supply caused by fluctuations in the quantity of primary gas 7 produced, and thus either the pressure or the amount in the total gas flow 14, can be compensated for by deducting excess gas and, at the actual gas utilization unit 9, to one Vibration resistant alternative gas utilization unit 15, eg a surplus burner or a pressure tank, are guided. However, this inevitably bypasses part of the product gas energy at the main utilization unit 9, which reduces the efficiency of the conversion of primary fuel to the desired final energy.

Gas storage facilities have already been proposed to offset the fluctuations in the primary gas produced. However, these require additional investment, which may be significant due to the risk of condensation of water and hydrocarbons from the product gas and associated pollution / corrosion. Excess burners also reduce the amount of primary gas produced without fully exploiting their energy content.

Object of the present invention is therefore to overcome the disadvantages of the prior art, so that the total product gas amount 14 of the main gas utilization unit 9 to supply and completely compensate for the naturally occurring by the fuel input fluctuations in the product gas quantity.

This object is achieved in accordance with the invention in that, in a method mentioned at the outset, the fluctuations in the product gas quantity resulting from the fuel feed and fuel composition are compensated by a rapidly reacting, variable product gas recirculation 13 into the combustion reactor 4. The product gas stream recirculated into the combustion reactor is used, so to speak, as a sink for the fluctuating proportion of the total product gas quantity. - A -

The operating temperature of the combustion reactor or of the gas generating reactor reacts only very slowly due to the high heat capacity of the bed material and the reactor walls to changes in the recirculated gas amount, the higher-frequency fluctuations in the product gas quantity are absorbed by the thermal capacity of the fluidized bed system. It should be noted that the recycled in the time average product gas amount in the inventive method is not greater than the recirculated in the prior art product gas quantity, however, in the inventive method, a constant total product gas amount 14 is provided, while in the methods of the prior art in the Alternate gas utilization unit product gas must either be consumed or costly stored to provide a constant total product gas flow 14. In the process according to the invention, the product gas consumed in the alternative gas utilization according to the prior art is available for the main gas utilization. This can either increase the load of the main gas use, or it can be relieved the gas generation. The efficiency increases or the specific fuel input decreases in relation to the main gas use.

Whenever "fast" (for a control valve) or "fast reacting" (for product gas recirculation) is mentioned below, this is a term familiar to a person skilled in the art, which is used both in German and in English In the present case, this means, in particular, that a fast-reacting variable product gas recirculation must be fast enough to be able to control the product gas fluctuations, depending on the plant and operating conditions, the knowledge of the skilled person will be able to take appropriate measures In connection with "fast-reacting", it is also clear to the person skilled in the art what is meant by "variable" product gas recirculation, namely that the product gas recirculation is variable to such an extent that a complete product gas recirculation takes place with the open control valve 18, while no product gas recirculation takes place with the control valve 18 closed Was known , a partial recycling of product gas, cf. See also Figure 1 with respect to line 13. Here, the partial flow 13 of the conditioned product gas is adjustable to the operating temperature of the gas regardless of the fluctuating fuel properties. According to the invention, a fast control valve is now used, so that the entire product gas quantity can be supplied to the main gas utilization unit and the fluctuations of the product gas quantity, which naturally occur due to the introduction of fuel, are completely compensated. The term "partially" refers to the recirculation of product gas to control the temperature in the fluidized bed system and is known in the art. "Partial" is to be understood as meaning that neither the entire product gas is recirculated - in which case no gas utilization would be possible - nor any product gas is recirculated - in which case no regulation of the produced product gas quantity is possible. In practice, the amount of gas to be recycled will depend on variations in the amount of product gas and will be between about 0.5 and 25% by mass of the total product gas, wet fuel and adverse conditions above it. For good conditions, a return amount in the range from 2 to 15% by weight, preferably from 3 to 10% by weight, is to be expected.

Preferably, in the method according to the invention, the system pressure of the product gas before the product gas compressor 19 is kept constant by the variable product gas recirculation 13 in the combustion reactor 4, whereby a constant flow rate at constant pressure is available on the pressure side of the product gas compressor 19. Due to the constant pressure maintained on the suction side of the product gas compressor 19 so the necessary control effort for the product gas compressor 19 can be kept low.

It is also favorable if the temperature in the combustion reactor 4 is adjusted by the fuel quantity supplied to the gas generation reactor 2, whereby increased production of product gas caused by the increased supply of fuel, with constant gas demand of the gas utilization device 9, via the partial return 13 of product gas into the combustion reactor 4 directly affects the average amount of product gas recycled to the combustion reactor. This provides a clearly understandable automatic control between the manipulated variable amount of fuel and the control variable operating Gaserzeu ^¬ ger represents the temperature in the combustion reactor 4 is the Control variable fuel quantity regulated to a desired value.

In a further preferred embodiment of the method according to the invention, the amount of air to the combustion reactor is adjusted by an automatic control so that the air-to-fuel ratio in the combustion reactor 4 and the residual oxygen content of the exhaust gas of the combustion reactor 4 are kept at a desired value.

According to a preferred embodiment of the method according to the invention, the temperature averaged over a suitable period of time in the gas generating reactor 2 determines the desired value for the temperature in the combustion reactor 4. This achieves stable operation at the desired temperature in the gas generating reactor 2. Periods over which the temperature in the gas generating reactor is averaged to determine the setpoint for the temperature in the combustion reactor are appropriate when excessive spikes or too low temperatures, such as those encountered during start-up or malfunctions, are avoided. In any case, the appropriate period will in any case be a multiple of the period of product gas fluctuations, in practice such a period will be between about 15 minutes to one hour, or even more, depending on external conditions and depending on the setting of the plant.

According to another aspect of the present invention there is provided an apparatus for providing a constant amount of product gas from a fluidized bed gasification system comprising a fluidized bed system coupled via at least one circulating bed material stream 5 comprising at least one gas generating reactor 2 having a metered fuel supply (1, 20) and at least one combustion reactor 4, a gas conditioning system 8 arranged in the gas generating reactor 2 and a connected gas use 9 with upstream product gas compressor 19, and a partial recycle 13 of product gas for regulating the temperature in the fluidized bed system, characterized in that in the partial recirculation 13 of product gas for Combustion reactor 4, a product gas recirculation compressor 17 and a fast control valve 18 are arranged. The arrangement according to the invention comes with a smaller number of appa- advise than the currently known arrangements and allows the supply of the entire non-recirculating product gas to the actual gas utilization unit 9. The inventive arrangement is therefore more cost-effective to purchase and more efficient in operation than the previously known arrangements.

It is preferable if the product gas recirculation compressor 17 in the partial recirculation 13 of product gas to the combustion reactor 4, the fast control valve 18 is connected upstream.

Conveniently, on the other hand, if the product gas recirculation compressor 17 in the partial recirculation 13 of product gas to the combustion reactor 4, the fast control valve 18 is connected downstream.

In particularly preferred variants, the fast control valve 18 in the partial recirculation 13 of product gas to the combustion reactor 4 can also be omitted, namely when the product gas recirculation compressor 17 can be controlled sufficiently fast to compensate for the product gas volume fluctuations.

According to a further preferred embodiment, the partial recirculation 13 branches from product gas to the combustion reactor 4 before the product gas pre-compressor 19 from the product gas stream. Thus, the suction-side system pressure of the product gas pre-compressor 19 can be directly influenced via the controlled system 13, 17, 18.

It is preferable if the partial recirculation 13 branches from product gas to the combustion reactor 4 in the gas conditioning 8 from the product gas stream. Thus, the product gas stream to be recirculated is only subjected to a part of the gas purification steps (rough cleaning), the more elaborate fine purification steps are undertaken only for the gas to be supplied to the gas utilization unit 9.

According to another preferred embodiment of the present invention, the partial recycle 13 branches from product gas to the combustion reactor 4 after

Product gas pre-compressor 19 from the product gas stream. This may be favorable with a suitable characteristic curve of the product gas pre-compressor 19. In this case, the pressure-side system pressure of the product gas pre-compressor 19 can be directly influenced via the controlled system 13, 17, 18.

With reference to the appended FIG. 2, the invention will fertil now explained in more detail.

In the method according to the invention, the entire product gas quantity 14 which is not attributable to the main gas utilization unit 9 is made available, namely as a constant quantity of gas at constant pressure. The main gas use unit 9 determines the necessary amount of gas by its consumption and requires a certain pre-pressure (for example, a gas engine sucks in gas, the set value for the engine load is given). The product gas recycle compressor 17 and a fast control valve 18 upstream or downstream of the product gas recycle compressor (in FIG. 2, the fast control valve 18 is connected downstream of the product gas recycle compressor 17) regulate the product gas pressure in stream 16 to a constant setpoint. The main product gas compressor 19 becomes quasi-rigid, i. with a very slow control characteristic, which makes it possible to participate in intended load changes of the entire system, operated, and raises the pressure of the stream 16 in the entire product gas stream 14 to the necessary form of the gas utilization unit. 9

By the Brennstoffdosiereinrichtung 20 in the gas generating reactor 2, the temperature in the combustion reactor 4 is controlled to a desired value. This is possible because a higher fuel quantity leads to more gas production in the gas generating reactor 2 and due to the fast control valve in the partial recirculation 13 of the entire product gas stream 14 can be kept constant, which passes through the partial feedback 13 directly more gas into the combustion reactor 4.

The desired value for the temperature in the combustion reactor 4 is determined with a slow control characteristic on the basis of the optionally averaged over a suitable period temperature in the gas generating reactor 2. Thus, the system can be operated as before at a practically constant temperature in the gas generating reactor 2. The method also works when the product gas to be recirculated downstream of the main product gas compressor 19, i. is removed from the stream 14 instead of stream 16.

The inventive method also works when the product gas to be recirculated is taken out of the gas conditioning at any point rather than from stream 16. The method may be where the amplitude of the fluctuations or other speak technical or economic reasons for it, if necessary also be combined with a gas storage.

Claims

Patent claim:

A method of providing a constant volume of product gas from a fluidized bed gasification plant comprising a fluidized bed system coupled via at least one circulating bed material stream (5) comprising at least one gas generating reactor (2) having a metered fuel supply

(1, 20) and at least one combustion reactor (4), a gas conditioning (8) arranged in the product gas stream (7) coming from the gas generating reactor (2) and a connected gas use (9) with upstream product gas compressor (19), as well as a partial recycling ( 13) of product gas for regulating the temperature in the fluidized bed system, characterized in that the resulting from the fuel supply and fuel quality fluctuations of the product gas quantity produced by a fast-reacting, variable product gas recirculation

(13) are balanced in the combustion reactor (4).

2. The method according to claim 1, characterized in that the system pressure of the product gas before the product gas compressor (19) by the variable product gas recirculation (13) in the combustion reactor (4) is kept constant and thus on the pressure side of the product gas compressor (19) a constant flow rate available at constant pressure.

3. The method according to claim 1 or 2, characterized in that the temperature in the combustion reactor (4) by the gas generating reactor (2) supplied amount of fuel is adjusted, which caused by increased supply of fuel increased production of product gas at constant gas demand of Gas utilization device (9) via the partial return (13) of product gas in the combustion reactor (4) directly on the average recirculated to the combustion reactor amount of product gas.

4. The method according to any one of claims 1 to 3, characterized in that the averaged over a suitable period temperature in the gas generating reactor (2) determines the desired value for the temperature in the combustion reactor (4).

5. Apparatus for providing a constant quantity of product gas from a fluidized bed gas generating plant, comprising a fluidized bed system coupled via at least one circulating bed material flow (5) comprising at least one gas generating reactor (2) with a metered fuel feed (1, 20) and at least one combustion reactor (4), a gas conditioning (8) arranged in the product gas stream (2) coming from the gas generating reactor (2) and a connected gas utilization (9) with upstream product gas compressor (19) and a partial recycling (13) of product gas for regulating the temperature in the fluidized bed system, characterized in that in the partial recirculation (13) of product gas to the combustion reactor (4) a product gas recycle compressor (17) and a fast control valve (18) are arranged.

6. The device according to claim 5, characterized in that the product gas recirculation compressor (17) in the partial return (13) of product gas to the combustion reactor (4), the fast control valve (18) is connected upstream.

7. The device according to claim 5, characterized in that the product gas recirculation compressor (17) in the partial return (13) of product gas to the combustion reactor (4), the fast control valve (18) is connected downstream.

8. The device according to claim 5, characterized in that when using a controllable product gas recirculation compressor (17) with fast control behavior in the partial recirculation (13) of product gas to the combustion reactor (4), the fast control valve (18) can be omitted.

9. Device according to one of claims 5 to 8, characterized in that the partial return (13) of product gas to the combustion reactor (4) before the product gas pre-compressor (19) branches off from the product gas stream.

10. The device according to claim 9, characterized in that the partial return (13) of product gas for incineration reactor (4) in the gas conditioning (8) branches off from the product gas stream.

11. Device according to one of claims 5 to 8, characterized in that the partial return (13) of product gas to the combustion reactor (4) after the product gas pre-compressor (19) branches off from the product gas stream.