METHOD AND APPARATUS FOR PURIFYING AND COOLING BIOMASS SYNGAS

Abstract

A method for purifying and cooling biomass syngas. The method includes: 1) cooling biomass syngas to 520-580 C., and recycling waste heat to yield a first steam; then subjecting the biomass syngas to cyclone dust removal treatment; and further cooling the biomass syngas to a temperature of 210 C., and recycling waste heat to yield a second steam; 2) removing a portion of heavy tar precipitating out of the biomass syngas during the second-stage indirect heat exchange; 3) carrying out dust removal and cooling using a scrub solution, to scrub off most of dust, tar droplets, and water soluble gases from the biomass syngas after the heat exchange and dust removing treatment; and 4) conducting deep removal of dust and tar with a wet gas stream, to sweep off remains of dust and tar fog in the scrubbed biomass syngas.

Claims

1. A method for purifying and cooling biomass syngas, the method comprising: 1) cooling biomass syngas having a temperature of 950 C. or higher and a pressure of 3.0 mPa or higher from a fluidized bed gasifier to a temperature of 520-580 C. using a first-stage indirect heat exchange, to yield a first steam; subjecting the biomass syngas to cyclone dust removal treatment; cooling the biomass syngas to a temperature of 210 C. using a second-stage indirect heat exchange, to yield a second steam and heavy tar; 2) removing the heavy tar; 3) washing and cooling the biomass syngas using a scrub solution, to scrub off dust, tar droplets, and water-soluble gases from the biomass syngas, wherein a temperature of scrubbed biomass syngas is between 43 and 47 C.; and 4) conducting deep removal of dust and tar with a wet gas stream, to remove dust and tar in the scrubbed biomass syngas, and allowing the pressure to drop to 0.3-1 mPa, to obtain a cleaned biomass syngas having a dust and tar content of less than 10 mg/Nm3, and a temperature of below 45 C.

2. The method of claim 1, wherein in 1), during the first-stage indirect heat exchange, the biomass syngas is cooled to 550-570 C.; and during the second-stage indirect heat exchange, the biomass syngas is cooled to 65-95 C.

3. The method of claim 1, wherein in 1), during the first-stage indirect heat exchange, the biomass syngas is cooled to 555-565 C.; and during the second-stage indirect heat exchange, the biomass syngas is cooled to 65-75 C.

4. The method of claim 1, wherein in 1), the pressure of the first steam is 6.0-9.8 mPa, and the pressure of the second steam is 0.5-0.8 mPa.

5. The method of claim 3, wherein in 1), the pressure of the first steam is 6.0-8.5 mPa, and the pressure of the second steam is 0.5-0.8 mPa.

6. The method of claim 1, wherein in 1), the first steam generated is fed back to the fluidized bed gasifier, and used as a gasifying agent of a biomass fuel.

7. The method of claim 3, wherein in 1), the first steam generated is fed back to the fluidized bed gasifier, and used as a gasifying agent of a biomass fuel.

8. The method of claim 1, wherein in 1), the biomass syngas output from the fluidized bed gasifier is controlled to have a temperature of 1000-1200 C., a pressure of 3.0-4.0 mPa, a dust content of <20 g/Nm.sup.3, and a tar content of <3 g/Nm.sup.3.

9. The method of claim 3, wherein in 1), the biomass syngas output from the fluidized bed gasifier is controlled to have a temperature of 1000-1200 C., a pressure of 3.0-4.0 mPa, a dust content of <20 g/Nm.sup.3, and a tar content of <3 g/Nm.sup.3.

10. The method of claim 1, wherein the second steam is used in 4) as a wet gas stream to sweep off the dust and tar in the biomass syngas.

11. The method of claim 3, wherein the second steam is used in 4) as a wet gas stream to sweep off the dust and tar in the biomass syngas.

12. An apparatus for purifying and cooling biomass syngas, the apparatus comprising: an integrated heat exchange and dust removal device; a packed tower scrubber; and a wet electrostatic precipitator; wherein the integrated heat exchange and dust removal device comprises a first heat exchanger, a cyclone separator, and a second heat exchanger connected in compact tandem in sequence; and a gas inlet of the first heat exchanger is connected to a syngas outlet of a fluidized bed gasifier, a gas outlet of the second heat exchanger is connected to a gas inlet of the packed tower scrubber, a gas outlet of the packed tower scrubber is connected to an input port of the wet electrostatic precipitator, and an output port of the wet electrostatic precipitator is connected to a gas inlet of a gas tank.

13. The apparatus of claim 12, wherein a steam outlet of the first heat exchanger is connected to a gasifying agent inlet of the fluidized bed gasifier via a first steam conveying pipe.

14. The apparatus of claim 12, wherein a steam outlet of the second heat exchanger is connected to a wet gas stream inlet of the wet electrostatic precipitator via a second steam conveying pipe.

15. The apparatus of claim 13, wherein a steam outlet of the second heat exchanger is connected to a wet gas stream inlet of the wet electrostatic precipitator via a second steam conveying pipe.

16. The apparatus of claim 12, wherein a dust outlet at a bottom of the cyclone separator is connected to a feed inlet of a bin pump, and a feed outlet of the bin pump is connected to an ash storage tank.

17. The apparatus of claim 13, wherein a dust outlet at a bottom of the cyclone separator is connected to a feed inlet of a bin pump, and a feed outlet of the bin pump is connected to an ash storage tank.

18. The apparatus of claim 12, wherein a tar outlet at a bottom of the second heat exchanger is connected to a feed inlet of a tar trough.

19. The apparatus of claim 13, wherein a tar outlet at a bottom of the second heat exchanger is connected to a feed inlet of a tar trough.

20. The apparatus of claim 12, wherein the output port of the wet electrostatic precipitator is further connected to a gas inlet of a tail gas incinerator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention is described hereinbelow with reference to accompanying drawings, in which the sole FIGURE is a schematic diagram of an ultrahigh-pressure cooling and purification apparatus for biomass syngas in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] For further illustrating the invention, experiments detailing a method and apparatus for purifying and cooling biomass syngas are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

[0032] The sole FIGURE shows an ultrahigh-pressure cooling and purification apparatus for biomass syngas for oil production. The apparatus comprises an integrated heat exchange and dust removal device 2, a packed tower scrubber 3 and a wet electrostatic precipitator 4. The integrated heat exchange and dust removal device 2 has an overall structure comprising sequentially a high-temperature heat exchanger 2a, a cyclone separator 2b, and a low-temperature heat exchanger 2c connected in compact tandem. A gas inlet 2-1 of the high-temperature heat exchanger 2a is connected to a syngas outlet 1-1 of a fluidized bed gasifier 1, a gas outlet 2-2 of the low-temperature heat exchanger 2c is connected to a gas inlet 3-1 of the packed tower scrubber 3, a gas outlet 3-2 of the packed tower scrubber 3 is connected to an input port 4-1 of the wet electrostatic precipitator 4, and an output port 4-2 of the wet electrostatic precipitator 4 is connected to a gas inlet 5-1 of a high-pressure gas tank 5, which is a spherical ultrahigh-pressure gas tank. A high-pressure steam outlet of the high-temperature heat exchanger 2a is connected to a gasifying agent inlet 1-2 of the fluidized bed gasifier 1 via a high-pressure steam conveying pipe 6. A low-pressure steam outlet of the low-temperature heat exchanger 2c is connected to a wet gas stream inlet 4-3 of the wet electrostatic precipitator 4 via a low-pressure steam conveying pipe 7. A dust outlet 2-3 at a bottom of the cyclone separator 2b is connected to a feed inlet 9-1 of a bin pump 9, and a feed outlet 9-2 of the bin pump 9 is connected to an ash storage tank 10. A tar outlet 2-4 at a bottom of the low-temperature heat exchanger 2c is connected to a feed inlet 11-1 of a tar trough 11. The output port 4-2 of the wet electrostatic precipitator 4 is further connected to a gas inlet 8-1 of a tail gas incinerator 8.

[0033] A process implemented with the above equipment is as follows. A high-temperature ultrahigh-pressure biomass syngas output from the fluidized bed gasifier 1 is controlled to have a temperature of 1000-1200 C., a pressure of 3.0-4.0 mPa, a dust level of <20 g/Nm.sup.3, and a tar content of <3 g/Nm.sup.3. The high-temperature ultrahigh-pressure biomass syngas is led out via the syngas outlet 1-1 at a top of the gasifier 1 after the slag solidification treatment in the gasifier, and then enters the integrated heat exchange and dust removal device 2. The biomass syngas is subjected to a first-stage indirect heat exchange in the high-temperature heat exchanger 2a to cool the high-temperature ultrahigh-pressure biomass syngas output from the gasifier 1 to 520-580 C., preferably to 550-570 C., and further preferably to 555-565 C. The high-pressure steam of 6.0-9.8 mPa and preferably 6.0-8.5 mPa generated during the waste heat recovery is delivered to the gasifier 1 and used as a gasifying agent of a biomass fuel. Subsequently, the high-temperature ultrahigh-pressure biomass syngas experiences a cyclone dust removal treatment by the cyclone separator 2b in the integrated heat exchange and dust removal device 2, and then enters the low-temperature heat exchanger 2c for a second-stage indirect heat exchange, such that the biomass syngas is further cooled to a temperature of 210 C., preferably to 65-95 C., and more preferably to 65-75 C. in the integrated heat exchange and dust removal device 2. The low-pressure steam of 0.5-0.8 mPa generated during the waste heat recovery is supplied to the exterior. A portion of heavy tar precipitating out of the biomass syngas upon cooling during the second-stage indirect heat exchange process flows via the tar outlet 2-4 at the bottom of the low-temperature heat exchanger 2c into the tar trough 11, and removed by collection in the tar trough 11. Next, the cooled and preliminarily-dedusted biomass syngas exits from the integrated heat exchange and dust removal device 2 via the gas outlet 2-2, and enters the packed tower scrubber 3 via the gas inlet 3-1 of the packed tower scrubber 3, where the biomass syngas is further dedusted and cooled by using an alkaline scrub solution such as caustic soda and a filler such as zeolite, to scrub most of the dust, tar droplets, and water soluble gases off from the biomass syngas, in which the temperature of the scrubbed biomass syngas is cooled to 43-47 C. Finally, the scrubbed biomass syngas is led out of the packed tower scrubber 3 via the gas outlet 3-2, and input into the wet electrostatic precipitator 4 via the input port 4-1 of the wet electrostatic precipitator 4; and the low-pressure steam generated during the second-stage indirect heat exchange process is also introduced therein as a wet gas stream for sweeping the dust and tar fog in the biomass syngas. The deep removal of dust and tar allows a small amount of dust and tar fog remaining in the biomass syngas to be removed, and allows the pressure of the biomass syngas to drop to 0.3-1 mPa, so as to obtain a cleaned biomass syngas having a dust and tar content of less than 10 mg/Nm.sup.3, and a temperature of below 45 C., with a sensible heat recovery rate being greater than 80%. Moreover, the qualified biomass syngas is delivered to the ultrahigh-pressure gas tank 5 via the gas inlet 5-1 of the ultrahigh-pressure gas tank 5 for storage or for use in a downstream procedure. The exhaust gas is disposed in the tail gas incinerator 8 connected in parallel with the ultrahigh-pressure gas tank 5, during which a low-pressure steam is generated and supplied to the exterior. The dust separated by the cyclone separator 2b in the integrated heat exchange and dust removal device 2 is collected by the bin pump 9 and then pneumatically conveyed to the ash storage tank 10 for storage and later reasonable utilization. The positive pressure of 0.3 mPa or higher remains at the gas inlet 5-1 of the high-pressure gas tank 5, to ensure that the integrated heat exchange and dust removal device 2, the packed tower scrubber 3, the wet electrostatic precipitator 4 and the ultrahigh-pressure gas tank 5 can operate under an ultrahigh pressure.

[0034] Unless otherwise indicated, the numerical ranges involved in the invention include the end values. While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.