Method and system for gasification of biomass

Abstract

A system for gasifying biomass is disclosed. The system comprises a water storage tank, a water pump, a heat exchanger, a plasma torch heater, a gasifier, an ash cooler, a spray tower, a dust collector, a deacidification tower, and a desiccator. The water storage tank is connected to the water inlet of the heat exchanger; the vapor outlet of the heat exchanger is connected to the vapor inlet of the plasma torch heater; the vapor outlet of the plasma torch heater is connected to the vapor nozzle of the gasifier; the ash outlet of the gasifier is connected to the ash inlet of the ash cooler; the gas outlet of the gasifier is connected to the gas inlet of the spray tower; and the gas outlet of the spray tower is connected to the gas inlet of the heat exchanger.

Claims

1. A system for gasifying biomass, the system comprising: a) a water storage tank (10); b) a water pump (9); c) a heat exchanger (12), said heat exchanger (12) comprising a water inlet, a vapor outlet, a gas inlet, and a gas outlet; d) a plasma torch heater (5), said plasma torch heater (5) comprising a vapor inlet and a vapor outlet; e) a gasifier (6), said gasifier (6) comprising a vapor nozzle, an ash outlet, and a gas outlet; f) an ash cooler (7), said ash cooler (7) comprising an ash inlet; g) a spray tower (11), said spray tower (11) comprising a gas inlet and a gas outlet; h) a dust collector (13); i) a deacidification tower (14); and j) a desiccator (15); wherein said water storage tank (10) is connected to said water inlet of said heat exchanger (12) via said water pump (9); said vapor outlet of said heat exchanger (12) is connected to said vapor inlet of said plasma torch heater (5); said vapor outlet of said plasma torch heater (5) is connected to said vapor nozzle of said gasifier (6); said ash outlet of said gasifier (6) is connected to said ash inlet of said ash cooler (7); said gas outlet of said gasifier (6) is connected to said gas inlet of said spray tower (11); said gas outlet of said spray tower (11) is connected to said gas inlet of said heat exchanger (12); and said gas outlet of said heat exchanger (12) is connected to said dust collector (13), said deacidification tower (14), and said desiccator (15) in series.

2. The system of claim 1, wherein said system further comprises a plurality of vapor nozzles, said vapor nozzles are arranged on said gasifier (6) and grouped into 3-4 height levels, and said vapor nozzles of each level are evenly and tangentially arranged along a circumferential direction.

3. The system of claim 1, wherein said system further comprises a nitrogen protecting device (4) connected to a feed inlet of said gasifier (6).

4. The system of claim 3, wherein said system further comprises a plurality of vapor nozzles, said vapor nozzles are arranged on said gasifier (6) and grouped into 3-4 height levels, and said vapor nozzles of each level are evenly and tangentially arranged along a circumferential direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described hereinbelow with reference to accompanying drawings, in which the sole FIGURE is a structure diagram of a system for gasification of biomass.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) For further illustrating the invention, experiments detailing a method and a system for gasifying biomass using water vapor are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

(3) As shown in the sole FIGURE, a system for indirect gasification of biomass using water vapor, comprises: a belt conveyer 1 for transporting the biomass, a hopper 2, a screw feeder 3, a gasifier 6 for transforming the biomass into a crude synthetic gas, a spray tower 11 for quenching the crude synthetic gas, a plasma torch heater 5 for supplying a high temperature superheated water vapor to the gasifier 6, a water storage tank 10 and a water pump 9 for providing a water source to the plasma torch heater 5, a heat exchanger 12 for comprehensive utilization of heat energy, and a dust collector 13, deacidification tower 14, and a desiccator 15 for later cleaning of the synthetic gas.

(4) An output end of the belt conveyer 1 is arranged above an inlet of the hopper 2, an outlet of the hopper 2 is connected to a feed inlet of the screw feeder 3, and a feed outlet of the screw feeder 3 is connected to a feed inlet of the gasifier 6.

(5) As a key device for transforming the biomass into synthetic gas, the gasifier 6 comprises: a casing, and a liner. The casing is air cooled jacket or water cooled jacket, and thermal insulated at a normal pressure; the liner is made of a material being refractory, anticorrosive, and insulated. The feed inlet of the gasifier 6 is designed on an upper part or an upper end, and the number of the feed inlet is two to four in compliance with the capacity, so that the biomass can be evenly fed into the gasifier 6 and a stable gas flow in the gasifier 6 is maintained. A nitrogen protecting device 4 is disposed at the feed inlet of the gasifier 6 to form a nitrogen sealing layer which can effectively prevent the crude synthetic gas from contacting with the outer atmosphere. A plurality of the vapor nozzles are arranged on the gasifier 6 and grouped into 3-4 height levels, and the vapor nozzles of each level are evenly and tangentially arranged along a circumferential direction. Thus, the high temperature superheated water vapor in the gasifier 6 forms an even and stable flow field, which is fully contacted and mixed with the biomass. An ash outlet is arranged on a bottom of the gasifier 6, and one or two ash outlets can be employed in compliance with the capacity, the ash discharged from the gasifier 6 is in a liquid state. The ash outlet is connected to an ash cooler 7 in which the liquid ash is transformed into a solid state. A gas outlet of the gasifier 6 is arranged on an upper part, or in a lower part, and is connected to a gas inlet of the spray tower 11 via a pipe.

(6) The spray tower 11 is a key device for quenching the crude synthetic gas, in which the crude synthetic gas is directly washed by a circulating cooling water to remove slags, alkali metal oxides, and other impurities in the crude synthetic gas. A gas outlet of the spray tower 11 is connected to a gas inlet of the heat exchanger 12; and a gas outlet of the heat exchanger 12, the dust collector 13, the deacidification tower 14, and the desiccators 15 are connected in series. A gas outlet of the desiccators 15 is connected to a gas storage tank 16 for storing a clean synthetic gas.

(7) The high temperature superheated water vapor sprayed into the gasifier 6 is transformed from soft water or desalted water in the water storage tank 10. An outlet of the water storage tank 10 is connected to a water inlet of the heat exchanger 12 via the water pump 9. The heat exchanger 12 is usually selected from scrapped boiler. A vapor outlet of the heat exchanger 12 is connected to a vapor inlet of the plasma torch heater 5, and a vapor outlet of the plasma torch heater 5 is connected to vapor nozzles of the gasifier 6 via pipes.

(8) The system also comprises the ash storehouse 8, the ash from the ash collector 7 and the spray tower 11 is transported to the ash storehouse 8 by manual or mechanical.

(9) A method for gasifying biomass using water vapor is described as follows: A) A ground biomass is successively transported to a gasifier 6 via a belt conveyor 1, a hopper 2, and a screw feeder 3 in turn, at the same time nitrogen is input from a nitrogen protecting device 4 into a feed inlet of the gasifier 6. When the biomass is a gray straw, for example twigs and roots of trees, a particle size of the biomass is controlled at 50 mm×50 mm below, and a water content of the biomass is controlled at 40 wt. % below. When the biomass is yellow straw, for example stalks of threshed grain, thatch, stalks of corns, and the particle size of the biomass can be relatively larger than 50 mm×50 mm B) A desalted water is output from a water storage tank 10 to a water inlet of the heat exchanger 12 via a water pump 9, and the desalted water exchanges heat with a crude synthetic gas input from a gas inlet of the heat exchanger, and a sensible heat is extracted by the desalted water, during which 0.4-0.6 Mpa of saturated vapor is produced, the saturated vapor is output from a vapor outlet of the heat exchanger 12 to a plasma torch heater 5 and transformed to a high temperature superheated water vapor. C) The high temperature superheated water vapor produced by the plasma torch heater 5 is at a temperature of 1200-1600° C., and is input into the gasifier 6 via a vapor nozzle. Operating parameters of the gasifier 6 are: 1200-1400° C. of a temperature, and 105-109 kPa of a pressure. A input speed of the high temperature superheated water vapor into the gasifier is controlled at 35-50 m/s, so that the biomass is fully contacted with the superheated water vapor in a descending process, after processes of desiccation, separation of volatile matters, pyrolysis, and evaporation, a crude synthetic gas and a liquid ash are produced. The crude synthetic gas is maintained in the gasifier 6 for 15-20 s, and an output speed of the crude synthetic gas from the gasifier is controlled at 15-20 m/s. D) The liquid ash produced in the gasifier 6 is at a temperature of 1200-1400° C., and is input into an ash cooler 7 via an ash outlet of the gasifier 6. After heat recovery, the liquid ash is cooled down to 150° C. below, and is delivered to an ash storehouse 8 for a comprehensive utilization. The crude synthetic gas produced from the gasifier 6 is at the temperature of 1200-1400° C. and is transported to a spray tower 11 via pipes. After being washed by the cold water, the temperature of the crude synthetic gas is dropped to 750-800° C., in which the high temperature slags are transformed into particles, and alkali metal oxides and part of acid gases are dissolved into the cold water and discharged from the spray tower 11, so that a primary synthetic gas is acquired. The cold water in the spray tower can be recycled after precipitation and filtration, and the dregs are transported to the ash storehouse 8. E) The primary synthetic gas from the spray tower 11 is input into a heat exchanger 12 via a gas inlet after being removed from slags, so that coke, ash, and corrosion are effectively eliminated in the heat exchanger 12. At the moment, the primary synthetic gas is still at a temperature of 750-800° C., after a recovery of sensible heat by the desalted water, the temperature is dropped to 260-320° C. The primary synthetic gas is transported from a gas outlet of the heat exchanger 12 to a dust collector 13 in which dust is removed from the primary synthetic gas, and the primary synthetic gas in an outlet of the dust collector 13 has a dust concentration of no more than 50 mg/Nm.sup.3. F) After dust removal, the primary synthetic gas is transported to a deacidification tower 14, in which harmful gases like H.sub.2S, COS, HCL, NH.sub.3, and HCN are removed. G) After deacidification, the primary synthetic gas is transported into a desiccator 15, in which the water is removed, and a clean synthetic gas is acquired. The clean synthetic gas is transported into a gas storage tank 16 via pipes and is stored for industrial application.

(10) After many times of tests and data detections, main components and characteristics thereof of the clean synthetic gas are shown in Table 1.

(11) TABLE-US-00001 TABLE 1 Main components and characteristics of clean synthetic gas Number Component Unit Value 1 CO % (vol.) 25-35 2 H.sub.2 % (vol.) 40-50 3 N.sub.2 + Ar % (vol.) 1.6-1.8 4 CO.sub.2 % (vol.) 15-20 5 CH.sub.2 % (vol.) 5-6 6 CnHm % (vol.) <2 7 Heat value of a synthetic gas (LHV) MJ/Nm.sup.3 12.5-13.4 8 Efficiency of a cooled gas % ~88.1

(12) As shown in Table 1, the clean synthetic gas produced by the method comprises 85% of a total content of CO and H.sub.2, a ratio of H.sub.2/CO is larger than 1, a heat value of the synthetic gas is 12.5-13.4 MJ/Nm.sup.3, and an efficiency of the cooled gas is about 88%. Thus, the synthetic gas can bring great commercial benefits, and is especially applicable in industries of the integrated biomass gasification cycle combination and the biomass liquid fuel.

(13) 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.