Patent application title: BIOMASS GASIFICATION DEVICE AND PROCESS
Jian Chao Zhang (Dalian City Liaoni, CN)
Yu Zhang (Dalian City Liaoni, CN)
IPC8 Class: AC10J372FI
Class name: Generators cupola accessories
Publication date: 2011-12-22
Patent application number: 20110308157
The invention is in the field of biogas production. In particular the
invention is directed to a process and apparatus for the conversion of
carbon and hydrogen containing materials into biogas (viz. a gas stream
comprising CH4) containing material and subsequent purification of the
resulting gas. According to the invention biogas is produced from carbon
and hydrogen containing starting material. The unpurified biogas is
subsequently purified by subjecting it to a filtration step, which
comprises feeding said biogas to at least one cyclone providing cyclone
action, at least one water filter where said biogas is washed with water
and at least one dry filter where said biogas is dry-filtered, thus
producing a purified biogas, followed by subjecting said purified biogas
to compression, preferably using a water ring compressor, followed by
feeding the compressed gas to a water-gas separator.
1. Process for producing biogas from carbon and hydrogen containing
starting material, comprising the steps of feeding said starting material
to a gasification device, thus producing an unpurified biogas, followed
by subjecting said unpurified biogas to a filtration step, which
comprises feeding said biogas to at least one cyclone providing cyclone
action, at least one water filter where said biogas is washed with water
and at least one dry filter where said biogas is dry-filtered, thus
producing a purified biogas, followed by subjecting said purified biogas
to compression, preferably using a water ring compressor, followed by
feeding the compressed gas to a water-gas separator.
2. Process according to claim 1, wherein said biogas is cooled in a heat exchanger after being washed in said water filter.
3. Process according to claim 1, wherein said cyclone action, said water washing and said dry-filtering are carried out consecutively.
4. Process according to claim 1, wherein said water filter and said at least one dry filter, and optionally a heat exchanger are contained in a single unit.
5. Process according to claim 1, wherein starting material is selected from agricultural waste or organic rubbish, preferably from corn stalk, rice stalk, wheat stalk, peanut hull, bean stalk, seed husk, bio weeds, leafs, branches, old paper, paper box, used disposable chopsticks, waste paper, waste flax or combinations thereof.
6. Apparatus for producing purified and dry biogas comprising a gasification unit, which is connected by one or more pipes to a cyclone, which cyclone is connected by one or more pipes to a washing unit, which is connected by one or more pipes to a heat exchanger, which is connected by one or more pipes to a dry filter, which is connected by one or more pipes to a water ring compressor, which is connected by one or more pipes to a gas-water separator.
7. Apparatus according to claim 6, wherein a filtering mesh is installed horizontally at the upper part inside said gas-water separator.
8. Apparatus for purifying a biogas stream comprising a compound filter unit, gas generator system connecting with cyclone separator, a gas compression delivery device and gas-water separation device, in particular a water ring compressor, the gas separator being connected with pressure-equalizing pipe, the apparatus further comprising a water ring compressor and a gas-water separator, said water ring compressor being equipped with pressure-equalizing pipe, wherein said compressor is connected to the bottom of the gas generator, said gas generator, gas surge tank, filter system, water ring compressor and gas-water separator are connected with each other through gas delivery pipeline, and the pressure vessel is connected with the delivery pipe network at the user end through a reducing valve, wherein one end of said pressure equalizing pipe is connected to the gas delivery pipeline at the inlet end of the water ring compressor, the other end is connected to the gas delivery pipeline at the outlet end of the gas-water separator, said gas-water separator being equipped with a discharging valve and fluid level gage.
9. Apparatus according to claim 8, further comprising a cyclone separator, said cyclone separator being connected with said compound filter unit by gas delivery pipeline, wherein a sewer valve is installed at the bottom of the cyclone separator and of the compound filter unit respectively, wherein said cyclone separator is a hollowed spheroid with an upper part that is wider than its lower part, an inlet and an outlet which are provided at its upper part, wherein said inlet is furnished along tangent direction on the wall of the said spheroid, and said outlet is furnished at the center or nearby the center of the top of the said spheroid, wherein said compound filter unit comprises an integrated structure of water bath sprayer, heat exchanger and dry filter, the gas delivery pipeline being connected to the inner of the structure and being connected to the inlet chamber of the heat exchanger from the upper part of the said water bath sprayer and being connected to the lower part of said dry filter from the outlet chamber of the heat exchanger, wherein said water bath sprayer is a vessel with spraying device, including water feeding and discharging pipes and gas delivery pipeline, a height of water being stored inside the water bath sprayer sufficient to submerge the outlet of feeding pipe, wherein the inlet of said compound filter is located substantially in the center of water bath sprayer and above the highest level of the water bath, the gas delivery pipeline for gas inlet being inserted into the water stored in the water bath sprayer from the said inlet.
10. Apparatus according to claim 9, wherein said heat exchanger includes an inlet chamber, an outlet chamber and a heat exchange zone; wherein said heat exchange zone includes cooling circulation water, an inlet and an outlet pipeline and a heat exchange pipe in contact with water, an inlet chamber and an outlet chamber in the heat exchange zone, which are separated by two separation boards at both ends, wherein the ends of the heat exchange pipe are connected with the inlet chamber and the outlet chamber respectively.
11. Apparatus according to claim 10, wherein said dry filter includes at least two layers as upper and lower, with insulating layer and gas delivery pipeline in between, further comprising a multitude of filter meshes in each layer, wherein the outlet of the compound filter unit is located at the upper part of dry filter.
12. Apparatus according to claim 6, wherein said compound filter unit, said water bath sprayer, said heat exchanger and said dry filter form an integral and compound structure, wherein a gas delivery pipeline is connected to the inner of the structure and goes to the inlet chamber of the heat exchanger from said water bath sprayer and then is connected to the lower part of said dry filter from the outlet chamber of the heat exchanger, wherein a heat insulating layer is present between said water bath sprayer and said dry filter, wherein said water bath sprayer is a vessel with spraying device, including water feeding and discharging pipes and gas delivery pipeline, wherein the height of water that is present inside the water is sufficient to cover the entrance of feeding pipe, wherein the inlet of the said compound filter unit is located essentially in the center of water bath sprayer and above the highest level of the water bath, the gas delivery pipeline for gas inlet is inserted into the water stored in the water bath sprayer from the said inlet.
13. Apparatus according to claim 6, wherein said heat exchanger includes an inlet chamber, an outlet chamber and a heat exchange zone, wherein said heat exchange zone includes cooling circulation water, inlet and outlet pipeline and heat exchange pipe soaked in water, inlet chamber and outlet chamber in the heat exchange zone are separated by two separation boards at both ends of it, and the two ends of the heat exchange pipe are connected with the inlet chamber and the outlet chamber respectively.
14. Apparatus according to claim 6, wherein at least one filter mesh is installed at the upper part inside the said gas-water separator, the inlet of which is installed under said filter mesh.
 The invention is in the field of biogas production. In particular
the invention is directed to a process and apparatus for the conversion
of carbon and hydrogen containing materials into biogas (viz. a gas
stream comprising CH4) containing material and subsequent
purification of the resulting gas.
 At present, fossil resources such as coal, oil and natural gas are still used as the main fuel to meet the global energy requirement. Most of the fuel emits large amount of harmful gas and smoke during combustion.
 Besides fossil resources, biomass may also serve as an energy source. Biomass is usually not directly combusted (as is often the case for fossil fuels), but is first converted into a suitable fuel under the removal of, for example, water. To this end, biomass may for example be gasified.
 During gasification, various kinds of biomass, including organic rubbish, are subjected to oxygen lacking conditions at an elevated temperature. The gas products of the gasification comprise flammable gases that are suitable fuels. In this way, organic waste materials may be converted into fuel, which decreases their impact on the environment. Moreover, since biomass and organic rubbish are resources never running out, they offer a renewable source of energy.
 A known disadvantage of gasification is that the produced flammable gas contains large amounts of dust, wood tar and wood vinegar. During gasification, wood tar is formed from the resin of, for example, pine tree. Wood tar has a high viscosity. Wood vinegar is an aqueous mixture of various organic compounds, in particular acetic acid and methanol. Especially the presence of wood tar is a major problem in the field of biomass gasification, because of its damaging nature to the equipment in which it is processed. This hinders the development of biomass energy.
 To remove at least part of the wood tar, the produced gas is purified by depositing and filtering operations.
 The produced (purified) gas is usually compressed before storage and delivery. Herein, it is required that the compressor is anti-explosive, and that the storage in the compressed state is also flameproof. The presence of wood tar in the gas is in particular disadvantageous during the (anti-explosive) compression of the gas.
 Despite the depositing and filtering operations to reduce the amount of wood tar, the produced gas usually still contains a small amount of wood tar. Under the pumping action of the compressor, the remaining wood tar may accumulate in the compressor. If a pressure ring compressor is used, the wood tar may in particular adhere to the inside wall and pressure ring of the air compressor when the gas is passing through the air compressor.
 To prevent a decrease in the working efficiency of the air compressor, it has to be cleaned regularly. This results in a down time of the entire gasification device, and in a great decrement of the gasification efficiency.
 Another disadvantage of present gasification devices is that, due to the efforts that need to be made to minimize the amount of wood tar in the produced gas, they have a complicated structure, a large land coverage, many gasification processing procedures, and a heavy workload of installation and maintenance. This results in the increment of processing costs and decrement of the gasification efficiency.
 Accordingly, there is still room for improvement in the gas purification filtering design.
 In view of the above shortcomings, the invention aims to present a biomass gas purification device and purification process which has a compact structure, small land coverage, convenient installation and maintenance, simple technical process, low cost and/or high efficiency.
 It is further aimed that such biomass gas purification device produces a gas with a low content of wood tar, for example a content of lower than 2 mg/m3, preferably less than 1 mg/m3 even more preferably less than 0.5 mg/m3, typically from 0.1-0.4 mg/m3 (based on produced gas volume).
 Accordingly, the invention relates to a biomass gas purification device, comprising a cyclone separator that exits into a compound filter unit, which is connected to a water ring processor, which is connected to a water-gas separator, and which optionally comprises a pressure vessel.
 The cyclone separator, compound filter unit, water ring compressor, gas-water separator and optionally the pressure vessel are connected with each other by a gas delivery pipeline. Further, at the user end of an eventual pressure vessel may be connected a gas delivery pipeline through a reducing valve.
 In the process of the invention biomass is converted in a gasification device into an unpurified biogas. Such devices are known per se. Different types of gasifier can be used, for instance counter-current fixed bed reactor, co-current fixed bed reactor, fluidized bed reactor or entrained flow gasifier. A counter-current fixed bed ("up draft") gasifier comprises a fixed bed of biomass through which the gasification agent (steam, oxygen and/or air) flows in counter-current configuration. The ash is either removed dry or as a slag. The co-current fixed bed ("down draft") gasifier is similar to the counter-current type, but the gasification agent gas flows in co-current configuration with the fuel. Heat is added to the upper part of the bed, either by combusting small amounts of the fuel or from external heat sources. The produced gas leaves the gasifier at a high temperature, and most of this heat is often transferred to the gasification agent added in the top of the bed, resulting in an energy efficiency on level with the counter-current type. Since all tars must pass through a hot bed of char in this configuration, tar levels are much lower than the counter-current type. In a fluidized bed reactor, the fuel is fluidized in oxygen and steam or air. The ash is removed dry or as heavy agglomerates that defluidize. The temperatures are relatively low in dry ash gasifiers, so the fuel must be highly reactive; low-grade coals are particularly suitable. The agglomerating gasifiers have slightly higher temperatures, and are suitable for higher rank coals. Fuel throughput is higher than for the fixed bed, but not as high as for the entrained flow gasifier. The conversion efficiency can be rather low due to elutriation of carbonaceous material. Recycle or subsequent combustion of solids can be used to increase conversion. Fluidized bed gasifiers are most useful for fuels that form highly corrosive ash that would damage the walls of slagging gasifiers. Biomass fuels generally contain high levels of corrosive ash. In the entrained flow gasifier a dry pulverized solid, an atomized liquid fuel or a fuel slurry is gasified with oxygen (much less frequent: air) in co-current flow. The gasification reactions take place in a dense cloud of very fine particles. Most coals are suitable for this type of gasifier because of the high operating temperatures and because the coal particles are well separated from one another. The high temperatures and pressures also mean that a higher throughput can be achieved, however thermal efficiency is somewhat lower as the gas must be cooled before it can be cleaned with existing technology. The high temperatures also mean that tar and methane are not present in the product gas; however the oxygen requirement is higher than for the other types of gasifiers. Entrained flow gasifiers typically remove the major part of the ash as a slag as the operating temperature is well above the ash fusion temperature. A smaller fraction of the ash is produced either as a very fine dry fly ash or as a black colored fly ash slurry. Some fuels, in particular certain types of biomasses, can form slag that is corrosive for ceramic inner walls that serve to protect the gasifier outer wall. However some entrained bed type of gasifiers do not possess a ceramic inner wall but have an inner water or steam cooled wall covered with partially solidified slag. These types of gasifiers do not suffer from corrosive slags. Some fuels have ashes with very high ash fusion temperatures. In this case mostly limestone is mixed with the fuel prior to gasification. Addition of a little limestone will usually suffice for the lowering the fusion temperatures. The fuel particles must be much smaller than for other types of gasifiers. This means the fuel must be pulverized, which requires somewhat more energy than for the other types of gasifiers. By far the most energy consumption related to entrained bed gasification is not the milling of the fuel but the production of oxygen used for the gasification.
 In the gasification step the biomass is converted into unpurified biogas. This step is followed by subjecting the unpurified biogas to a filtration step, which comprises feeding said biogas to at least one cyclone providing cyclone action, at least one water filter where said biogas is washed with water and at least one dry filter where said biogas is dry-filtered, thus producing a purified biogas, followed by subjecting said purified biogas to compression, preferably using a water ring compressor, followed by feeding the compressed gas to a water-gas separator.
 FIG. 1a shows schematically one embodiment of a biomass gas compound filtering device according to the invention. FIG. 1b is a side view of FIG. 1a.
 FIG. 2a shows schematically one embodiment of a biomass gas purification device according to this invention. FIG. 2b is a top view of FIG. 2a.
 FIG. 3a shows schematically one an embodiment of a biomass gas gasification device according to this invention. FIG. 3b is a top view of FIG. 3a.
 Cyclone separators (or centrifugal collectors) are known in the art. In a cyclone separator, centrifugal or "cyclonic" action is used to separate dust or other particles from the gas stream. In a typical cyclone, a dust gas stream enters tangentially and is spun rapidly. Due to the centrifugal force of the circular flow, the dust particles move towards the wall of the cyclone. After striking the wall, the particles fall into a collector located underneath.
 The gas enters into the cyclone separator at A in FIG. 2 along tangent direction of the spheroid from the upper inlet of the cyclone separator, and spires down along its inner wall until it reaches the lowest point, indicated by B in FIG. 2. During the surging and soaking of the gas, at least part of the impurities such as dust, wood tar and wood vinegar are subsided to the bottom of the cyclone separator.
 The cyclone separator used in the invention is preferably a hollow cylinder with an upper part that is connected to a conical lower part, with the inlet and outlet located at the upper part. The inlet is placed along tangent direction on the wall of the said cylinder, the outlet is placed at the center or nearby the center of the top of the said cylinder, as indicated by C in FIG. 2. A sewer valve is installed at the bottom of the cyclone separator.
 Inside the cyclone, there may be present in the lower part a guiding pipe to assist the upwards moving gas flow to the central outlet in the upper part.
 The compound filter unit is an assembly of multiple units, preferably as an integrated structure, viz. a structure where the compounds are combined in a compact way. The compound filter unit comprises a water bath sprayer, a heat exchanger and a dry filter. The compound filter unit serves to further purify the gas stream, in particular via filtration. This is required to obtain a biogas product of the desired purity and quality.
 The gas delivery pipeline from the cyclone separator is connected to the compound filter unit, preferably to the inner of the structure. The pipeline first enters the water bath sprayer. This is a room, e.g. a vessel, having an internal volume of typically around 1-4 m3, to which is sprayed water, typically from the top of the unit. Water is present at a certain level, preferably at a level covering the feeding pipe. The feeding pipe preferably enters the water bath spraying unit somewhere in the middle part of this unit so that the distances to the wall of the unit are more or less the same from each point on the feeding pipe and the gas is discharged below the water bath level, as indicated by E in FIG. 1. A further section of the pipeline connects the water bath sprayer unit to the inlet chamber of the heat exchanger (F-G in FIGS. 1 and 2). The gas is cooled in the heat exchanger and leaves the heat exchanger at H. The outlet chamber of the heat exchanger is connected by a further pipe to the lower part of the dry filter, which it enters at I. In FIGS. 1 and 2, the dry filter is made up of two compartments, which are connected to each other by a pipe, through which the gas flows as indicated by J-K. The gas outlet of the compound filter unit is located at the upper part of the dry filter, indicated by L.
 The water bath sprayer unit usually is a vessel with a spraying device, including means for feeding water, discharging pipes and the gas delivery pipeline. There is a certain height of water stored inside the water bath sprayer. The inlet of the said compound filter unit is preferably located in the center of the water bath sprayer and below the highest level of the water bath. During operation, the gas delivery pipeline for gas inlet is usually inserted into the water stored in the water bath sprayer.
 The heat exchanger comprises an inlet chamber, an outlet chamber and a heat exchange zone; the said heat exchange zone includes cooling circulation water, inlet and outlet pipeline and one or more heat exchange pipes soaked in water. The inlet chamber and the outlet chamber in the heat exchange zone are separated by two separation boards at both ends of the heat exchange zone. The two ends of the one or more heat exchange pipes are connected with the inlet chamber and the outlet chamber respectively.
 The said dry filter comprises at least two structures as upper and lower, preferably with an insulating layer and gas delivery pipeline in between. Preferably, there are four or more filter meshes in each layer, more preferably 4-7 filtering meshes. These filters can be construed for instance from steel. Typical mesh sizes are 300-400 mesh (as used herein: number of openings per linear inch), preferably around 350.
 The said dry filter includes at least two layers as upper and lower, with preferably an insulating layer and gas delivery pipeline in between, there are four or more filter meshes in each layer, gas passes through the filter mesh into the next filter layer in the gas delivery pipeline; the outlet of the compound filter unit is located at the upper part of dry filter
 One or more sewer valves are installed at the bottom of the compound filter unit. Preferably, the inlet and the outlet chamber of the heat exchanger each contain a sewer valve.
 The design of a compound filtering unit according to the invention is more compact, with small land coverage and more convenient installation compared to conventional filtering units. Moreover, it integrates the wet filtering (water bathing, water spraying), the dry filtering (mesh filtering), and the cooling, resulting in a highly efficient and convenient technical process. Typically, in a compound filtering unit according to the invention, the purified gas has a tar elimination rate higher than 98%.
 After exiting the compound filter unit at L, the gas is fed to pump 100 for water separation. This pump is preferably a liquid ring compressor or water ring compressor. Water ring, or more generally liquid ring compressors are know in the art. A water or liquid ring pump is a rotating positive displacement pump. They are typically used as a vacuum pump but can also be used as a gas compressor. The function of a liquid ring pump is similar to a rotary vane pump the difference being that the vanes are an integral part of the rotor and churn a rotating ring of liquid to form the compression chamber seal. They are an inherently low friction design, with the rotor being the only moving part. For these reasons they are very suitable for pumping flammable/explosive gas mixtures. Sliding friction is limited to the shaft seals. Liquid ring pumps are typically powered by an induction motor. A suitable type of water ring compressor is the 2SY series manufactured by Zibo Vacuum Pump Factory Co., Ltd., China, having a variable power ranging from 11 kW to 355 kW. A typical gas flow from the compressor may range from 90 m3/h to 1800 m3/h. The discharge pressure after the compressor is typically 0.6 MPa or less, preferably from 0.3 MPa to 0.6 MPa. The compressor is cooled with water, typically having a temperature 10-18° C., preferably about 15° C. Water supply typically ranges from 60-400 dm3/min. The biogas has a temperature of 60-90° C., typically around 70° C., when entering the pump. After compression the temperature is typically from 12-18° C., preferably around 15° C.
 In a device and process of the invention, the compressor may serve two purposes: (1) as the flowing power in the device during the generation of gas and (2) as the power for compressing the purified gas.
 The gas discharging range of the water ring compressor is usually 90 m3/h-1800 m3/h. The maximum working pressure is typically 0.8 MPa.
 The gas-water separator is connected to the water ring compressor via the gas delivery pipeline. The compressed gas is cooled and as a result water is allowed to condensate and will flow down to the bottom of vessel 120, where it may be discharged by means of valve 123. The internal part of the water-gas separator can be dismantled to facilitate cleaning.
 In order to further improve the effects of gas-water separation and filtering, filtering mesh may be installed horizontally at the upper part inside the gas-water separator. The gas inlet is preferably installed below the said mesh.
 As a better design, the filtering mesh 121 of the said gas-water separator is of a funnel type, enabling it with larger filtering area while resulting in the rapid dropping of filtered water to improve the filtering efficiency. Typical mesh sizes range from 300-400, preferably around 350. The gas-water separator is equipped with discharging valve and fluid level gauge.
 The gas-water separator is usually connected to a pressure vessel for the storage of the purified gas. Usually, the pressure vessel is connected with a gas delivery pipeline at the user end through a reducing valve. In FIG. 3, gas discharge line 124 is connected to reducing valve 125, where the product gas may be reduced to a pressure of for instance 0.1 MPa for further use or storage.
 The invention further relates to a biomass gas gasification device, comprising, a blower, a gas generator, a cyclone separator, a compound filter unit, water ring processor, water-gas separator, and optionally a storage tank.
 A biomass gas gasification device of the invention comprises a blower, a gas generator and a biomass gas purification device as described hereinabove.
 The blower blows gas, usually air, into the gas generator.
 The gas generator is usually a biomass gasification device. Such devices are known in the art. The gas generator is connected to the biomass gas purification device by a gas delivery pipeline. It is in particular connected to the cyclone separator.
 The invention further relates to a process for biomass gas filtering by applying the above gas compound filtering unit. The process comprises water bathing, water spraying, heat exchanging and dry filtering procedures with the following features:
 With the aid of the pumping of the water ring compressor, biomass gas to be purified is transported through the cyclone separator and the compound filtering unit. The gas enters the compound filtering unit through the inlet of the water spraying chamber for water bathing. During this stage, part of impurities, including dust, wood tar and wood vinegar, are transferred to the water. After the spraying, the gas enters into the inlet chamber of the heat exchanger through the internal gas delivery pipeline between water bath sprayer and heat exchanger. It then goes along with the one or more heat exchanging pipes, which are immersed in cooling circulation water, and enters the outlet chamber. Subsequently, it enters the dry area through the gas delivery pipeline between heat exchanger and dry filter, it goes through the filter meshes (one by one), and finally exhausts through the upper outlet. Usually, regular drainage process are performed to the compound filtering device.
 The invention further relates to a process for the gasification of biomass, by applying the above biomass gas gasification device.
 The process for biomass gasification includes the following steps:
 (1) Gas generation from the biomass. Various agricultural wastes and organic rubbish may be used as the biomass material, for instance of agricultural origin or from municipal waste processing. Prior to gasification, the biomass is preferably dried until a water content of 20% or less by mass. During gasification, an oxygen lacking combustion is performed, using gas introduced by the blower and producing a flammable gas comprising CO, H2, CH4, C2H6, lower concentrations of other hydrocarbons (optionally substituted, in particular with O and/or N atoms) and/or foggy wood tar gas;
 (2) Gas purification, including filtering. With the pumping of the water ring compressor, the gas generated is transported through the cyclone separator and enters the compound filtration device through gas delivery pipeline. In the pipeline, the gas automatically cools down, which results in the deposit of impurities. In the compound filtration device the gas first enters the water filter of the compound filtration device, wherein various impurities in the gas, including dust and wood tar, are absorbed and deposited. Thereafter, the gas is introduced into the spray tank for further elimination of impurities. The gas is then cooled down and further purified over filter meshes. Via the water ring compressor, the gas enters the gas-water separator, wherein remaining water is separated from the gas.
 During the purification stage of the process, the cyclone and the compound filtering unit are usually drained on a regular basis to remove the impurities that have been separated from the gas.
 (3) Compressing and storage of gas. Under the action of the water ring compressor, the water is separated from the gas in the gas-water separator, where it is dry-filtered once more. The purified gas is compressed and may be stored in a pressure vessel.
 During the separation, the gas-water separator is usually drained on a regular basis to remove the separated water. To this end, the gas-water separator has the water level displayed on the liquid level gauge.
 The flowing of the gas generated is realized by the internal pressure of the blower and the pumping of water ring compressor. The water ring compressor pumps the gas into the pressure vessel with certain pressure to enable convenient collection and storage and delivery of gas. When the said water ring compressor does not work, the stop valve and the check valve prevent the purified gas from returning to the filtering system respectively or together.
 Compared to the existing technology, the beneficial effect of this invention is quite obvious:
 The invention is applying water ring compressor as the power unit for gas delivery and compression. Because of its working with water feature, the water ring compressor is sealed for its internal spaces by circulation water. Gas after filtering is with minim wood tar though, which will enter into the said circulation water and be taken outside of water ring compressor by circulation water, thus preventing wood tar deposit from adhering onto the inner wall of the compressor. This greatly decreases maintenance cost, enabling more steady and reliable gasification process;
 On the other hand, as the compressed gas of water ring compressor is basically in equal temperature, it is with better anti-explosive property, and safer for pumping out gas. Moreover, gas with dust, congealable gas and water-gas compound can be pumped out because there is no exhaust valve and friction surface; the sealing between its motion parts and fixed parts can directly be fulfilled by water sealing with good sealing effect.
 Meanwhile, water ring compressor is with simple and compact structure, small land coverage and relatively high rev of the pump. Normally it can be close-coupled with motor without applying reducing device, therefore it is with small structure dimension and large air displacement. The air displacement of the water ring compressor in this design is typically 90 m3/h-1800 m3/h.
 In a word, this set of biomass gasification device and gasification process integrates the generation, purification, filtering, compression, storage and delivery of gas, with more reasonable and compact structure, small land coverage, simpler, more efficient and safer process, more purified, cleaner and pollution free gas can be achieved. Especially, it has found a solution for the separation of wood tar, thus preventing effectively the inside of the pipes from corrosion, blocking and pollution to environment, complying with the environmental requirements of energy saving and lower emission, resulting in the gas quality in conformity with power generation standard and enabling a sustained working of the whole unit.
 Gas generated by gas generator, after the filtering by the filter, is purified and cooled down, the flowing of gas is realized by water ring compressor pumping, water ring compressor delivers gas into gas storage tank. Constant pressure intensity should be maintained for the gas inside the tank, the value of pressure intensity should ensure the pressure of the cooking utensils of the farthest users, the pressure of pressure vessel is less than around 0.1 MPa, control the gas pressure of the farthest locations under a certain pressure.
 Gas generated by gas generator is flowing upwards in the furnace, tar generated in oxidation layer and recovering layer can be heat split into permanent gas with low molecular weight, therefore the gas out of the furnace is with relatively small tar content, and after various filtering and water-gas separation, it is with reliable operation, reasonable matching of gas generation amount and gas amount, low material consumption, no need add any additives, heat value is as high as 1661 kcal/m3.
 FIG. 1a shows a schematic representation structure sketch map of an embodiment of a biomass gas compound filtering device according to the invention. FIG 1b is the left view of FIG. 1.
 In FIG. 1a the following features are shown: 1 biomass gas compound filtering device; 2 water bath sprayer; 4 water spraying room; 3 heat exchanger; 6 water filter; 10 inlet chamber; 11 water outlet; 12 cooling circulation water; 13 heat exchanging pipe; 14 water inlet; 15 outlet chamber; 16, 17 separation board; 20 dry filter; 21 filtering layer; 22 separation layer; 30 thermal insulation layer; 40, 50 drainage valve; 60 gas inlet; and 61 gas outlet.
 FIG. 2a shows a schematic representation of an embodiment of a biomass gas purification device invented according to this invention.
 FIG. 2b is the vertical view of FIG. 2a.
 In the FIG. 2a the following features are shown: 70 cyclone separator; 71 gas inlet; 72 gas outlet; 73 drainage valve; and 1 compound filtering device.
 FIG. 3a shows a schematic representation of an embodiment of a biomass gas gasification device invented according to this invention
 FIG. 3b is the vertical view of FIG. 3a.
 In the FIG. 3b the following features are shown: 80 blower; 90 gas generator; 70 cyclone separator; 73 drainage valve; 71 gas inlet; 72 gas outlet; 1 compound filtering device; 4 water spraying room; 5 dry filter; 3 heat exchanger; 100 water ring compressor; 110 pressure-equalizing pipe; 120 water-gas separator; 121 filtering mesh; 122 level meter; 123 drain valve; 124 discharge; and 125 reducing valve.
 By way of example a detailed description will now be given of the invention with reference to the figures. This description is not to be interpreted as limiting the scope of the invention.
 A biomass gasification device of the invention is shown in FIG. 3. It includes a blower 3, which has a typical power of 1.5 kW, one gas generator 90 with a height of typically 4,000 mm and a diameter of typically 1,800 mm. The height of oxygen chamber inside the heart is typically 1750 mm with an inner diameter of 1440 mm. A cyclone separator 70 is placed on the pipeline 71 of gas generator 90. The gas enters as indicated by the letter "A" in FIG. 2. The gas stream spirals down and enters hollow pipe at the bottom of the cyclone as indicated by the letter "B" in FIG. 2. Particles are collected in the bottom of the cyclone. The purified gas stream exits the cyclone as indicated by "C"; The filter unit has a water spraying room 4, a heat exchanger 3 and a dry filter 5. The gas stream enters the spraying room 4 below the water level as indicated by "E". The gas moves upwards by which it is further washed by water coming from sprayer 2. The gas then leaves the spraying/washing room 4 as indicated by the arrow at "F". Subsequently, the gas enters heat exchanger 3 as indicated by "G". This may be a shell/tube heat exchanger, cooling water entering through the shell via entry 14 as indicated by "M". Heating cooling water leaves through exit 40. The cooled gas leaves the heat exchanger as indicated at "H" and enters the dry filter as indicated by "I". It then follows the path indicated by the arrows and leaves the filter at exit 61 as indicated by the arrow at "L". A water ring compressor 100 is present and one gas-water separator 120. The gas-water separator 120 is in connection with one end of the pressure-equalizing pipe 110. The other end of the pressure-equalizing pipe 110 is connected to the gas delivery pipeline on inlet end of water ring compressor 100. The function of this pipe is to provide counterpoise for the water ring compressor at start up. It may be opened and closed by a valve. The gas-water separator 120 is equipped with a drain valve 123 and a level meter 122. It also includes several stop valves and check valves, a pressure vessel and the user end gas delivery pipeline network. There is a cooling water circulation system surrounding the heart of the said gas generator 90, its inlet and outlet are located on the bottom and top of the gas generator, respectively. Safety valves are installed respectively on gas generator 90, on the cyclone separator 70, and on the pressure vessel of the gas-water separator 120. Drainage valves are installed on the inlet chamber and the outlet chamber in the heat exchange zone 3 of unit 1, on dry filter 5 and on the bottom of the pressure vessel. The outlet end of the surge tank I is connected to smoke discharge valve 12, lower part of water filter 5 by Tee pipe; space between each joint parts is basically around 700 mm. The device can also be set according to actual requirements.
 The whole device integrates generation, purification, packing, storing and delivery of flammable gas with the following technical process:
 (1) Loading of biomass material: loading of agricultural waste or organic rubbish with water content less than 20% into the furnace of gas generator and press firm by upper suction and pressing disk. The said agricultural waste may include corn stalk, rice stalk, wheat stalk, peanut hull, bean stalk, seed husk and bio weeds, leaf and branches, etc. The said organic rubbish may include old paper, paper box, used disposable chopsticks, waste paper, waste flax and waste and old gloves etc. The water content of various mixtures is preferably less than 20%, more preferably less than 18%.
 (2) Anaerobic combustion and generation of flammable gas: after burning the material and under the precondition that the whole gas generation device is closed, air is blown into the gas generator by the blower to cause the anaerobic combustion inside the furnace and generate continuously the gas mixture comprising CO, H2, CH4, C2H6, and/or CnHm (n and m are integers; n>2; m>6). Meanwhile, it is possible to use more to drive the water ring compressor to pump gas into the furnace from the other end to let the gas flow.
 (3) Filtering and purifying to eliminate wood tar and dust etc. A compound filtering device is shown in FIG. 1. In this device, a dry and pure gas is obtained. Gas in the pipe first goes into water filter 6 for filtering. It is then further purified in the spraying tank 4; it is then cooled in a heat exchanger 3, and dry-filtering in various mesh filters (e.g. plant suction layer and filtering cotton etc. or filtering by steel mesh of 350 meshes). Steel meshes of 350 meshes are installed in the gas inlet and outlet of the dry filter respectively to further improve the filtering effect.
 (4) Gas Pressurization and storing: gas after the aforementioned filtering, purification and drying is pressurized into pressure vessel by water ring compressor with an operation pressure range of 0.1 MPa-0.8 MPa; set 90 m3 pressure vessel as an example, when the operation pressure of water ring compressor is 0.3 MPa and the operation pressure of the pressure vessel is also 0.3 MPa, then the gas stored in the vessel is 270 m3; when the operation pressure of water ring compressor 5 is 0.6 MPa and the operation pressure of the pressure vessel is also 0.63 MPa, then the gas stored in the vessel is 540 m3.
 Finally, gas in the pressure vessel is sent to delivery pipeline after reducing to typically 0.1 MPa by reducing valve, and then delivered to the user gas delivery pipeline for further reducing to 3000 Pa by a reducing valve. Then, it can be directly supplied to cooking utensils and can ensure continuous gas supply.
 In brief, the whole device can be understood vulgarly as: the blower blows air into gas generator, biomass material is carrying out energy conversion inside gas generator and flammable gas is formed, after the high efficient filtering as water bath filtering and dry filtering etc. the gas is loaded into a pressure vessel with a certain pressure intensity by water ring compressor. Before use of the clean and pure gas, the pressure reduced and the gas is delivered to user cooking utensils by delivery pipeline. As the filtering of the device is sufficient and highly efficient, the flame of the final generated gas is in pure sky blue.
 Gas generated by gas the generator, after the filtering by the filter, is purified and cooled down. The flowing of gas is realized by water ring compressor pumping. The water ring compressor delivers gas into a gas storage tank. Constant pressure intensity should be maintained for the gas inside the tank. The value of the pressure intensity should ensure the pressure of the cooking utensils of the farthest users. The pressure of the pressure vessel is less than around 0.1 MPa.
 Gas generated by gas generator is flowing upwards in the furnace, tar generated in oxidation layer and recovering layer can be heat split into permanent gas with low molecular weight. Therefore the gas out of the furnace is with relatively small tar content, and after various filtering and water-gas separation, it is with reliable operation, reasonable matching of gas generation amount and gas amount, and low material consumption. There is no need to add any additives. The heat value is as high as 1661 kcal/m3, each kg of material can be converted into a flammable gas of 2.0 m3. It can satisfy the continuous and sustained gas supplying for thousands of families.
 The above is only one specific implementation of this invention and the scope of the present invention is not limited thereto, as many modifications are conceivable.
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