WO2009129762A1

WO2009129762A1 - Method and device for reducing the fine dust in the exhaust gas during thermal gasification of stalky or lumpy biomass

Info

Publication number: WO2009129762A1
Application number: PCT/DE2008/000680
Authority: WO
Inventors: Christian Herlt
Original assignee: Christian Herlt
Priority date: 2008-04-22
Filing date: 2008-04-22
Publication date: 2009-10-29
Also published as: DE112008003917A5

Abstract

The invention relates to a method and a device for reducing the dust and ash content, in particular the fine dust content, of the gases arising during the thermochemical gasification of biomasses. The object of the present invention is to provide a very easily implemented method with a corresponding device for reducing the dust emission during the thermal gasification of biomass, in particular thermal gasification of whole bales made of stalky biomass from the field and coarse lumpy wood biomass, in that the generation of liquid slag and fine dust is reduced at the site of the gas generation. According to the invention, water or water vapor is introduced into the gasification chamber (2, 14) for reducing the fine dust in the fuel gas and in the exhaust gas during the thermal gasification of stalky or lumpy biomass in the form of bales, bundles, stacks or pellets, after the gasification has begun and as a function of the temperature in the gasification chamber (2, 14) in order to ensure a chamber temperature of 280 to 650 °C, or 450 to 800°C in the bales (1).

Description

Patent application

Name of the invention

Method and device for reducing the fine dust in the exhaust gas in the thermal gasification of chunky or lumpy biomass

description

The invention relates to a method and a device for reducing the dust and ash content, in particular the fine dust content of the gases resulting from the thermochemical gasification of biomass.

State of the art

Reducing the emission of particulate matter from biomass combustion plants has become an urgent concern in environmental protection. There are a variety of proposals and solutions for the use of exhaust gas filters of various types, washing facilities, cyclone separators, etc. These systems remove the dust-laden product gas, fuel gas or exhaust gas, a proportion of dust, but have no influence on the formation of dust.

Especially in biomass gasification plants of greater power for processing highly comminuted, fine-grained biomass, it is customary to work at temperatures that are so high that the ash is obtained as a liquid slag and so can be discharged. However, the fine particles of dust that form the fine dust, which form dust dust, go along with the product gas.

In DE 699 11 983 T2 it is proposed to add liquid ash to added, refractory fines and thus auszuschleusen from the gasification. This can be realized in entrained flow or fluidized bed gasification with correspondingly complex system technology. When gasification in small plants, in which the biomass is used in the form of whole bales of stalks, logs, etc., the addition of fines is much too expensive, the necessary mixing virtually impossible.

Gasification plants of smaller power are largely built so that the ashes contained in the biomass remain as completely as possible in the gasifier room, in ash rooms or settling chambers and are not discharged with the product gas. Systems of this type are known, for. B. for the gasification of whole straw bales according to WO 2005/040680 or for a larger amount of lumpy logs according to EP 0 935 731. In systems of this type the biomass to be gasified remains over a long period of time, up to many hours in the gasifier room and so The gasification process is much slower than in plants where the biomass is crushed and fed continuously. The combustion processes maintained in large gasification rooms are dependent on the combustion air guidance and thus vary in intensity locally and with time. Pyrolysis and gasification take place side by side. The ashes naturally contain whatever refractory components, fine particles can be held in the mechanical bond and be attached the micro ^¬ fine droplets of low-melting salts and oxides and so adhesively bonded.

In particular, in the whole-bales of straw, hay, hemp and other hemispherical material from the field form the first For a long time, the carbon fiber strands burning last as black fibers are a three-dimensional filter-like structure in which most of the ash is retained. The still resulting fine dust consists mainly of low-melting, sometimes melted or even evaporated salts and oxides from the many substances contained ash mixture, is therefore of extremely small grain size and difficult to deposit with known filter technology, especially in the normal for small heating, periodic operation ,

The ashes of the stalks contain many alkaline compounds, in particular salts, many of which are very hygroscopic, so that they can easily clog the tissues of the known exhaust gas filter. The addition of water causes the formation of alkalis and acids and these are the cause of corrosion on metallic and ceramic components of the plants.

Electrostatic precipitators must be operated at very high voltages because of the extreme fineness of the dust particles, which entails high costs and dangers.

The gas or exhaust gas cleaning from incinerators with gas scrubbing or quenching has also been known for some time. These are often found in the industrial sector, but in the field of building heating but too expensive and difficult to handle. There are problematic wastewater with different, part toxic, part unknown compounds. These must be evaporated or collected and spe ^¬ essential disposed of.

In addition, the chimney then increasingly shows a vapor plume, which is also undesirable.

It is also known, in addition to already always present water content of the biomass or coal, water or steam in the carburetor room to initiate and so Even modern high-performance gasification processes, such as disclosed in DE 199 25 316, make use of this possibility of obtaining more fuel gas. It is also proposed in the same patent to use a catalyst (limestone), but this is expensive and considerably increases the ash attack.

The method of addition of water is also applicable to wood gasification in small units, as explained for example in the patent CH 221697. It is intended to achieve a higher hydrogen content in the fuel gas. The supply of water or steam can only take place if sufficiently high temperatures exist in the gasification space. Accordingly, regulation is applied only in this aspect. A water or steam feed is used, comparable to a cooling of grates and reaction chambers, but also to lower the gasification temperature in order to avoid excessive temperatures, which wear out the technical equipment. In DE 10 2005 006 3005 maximum temperatures of below 1200 ⁰ C and minimum temperatures of 800 ° C are then specified.

A water or water vapor feed in the gasification of hemi-shaped biomass, z. As straw bales, has not been proposed, since it was expected that the known unfavorable combustion and gasification conditions will deteriorate by the cooling or water condensation on. Temperatures below 800 ^° C generally cause a higher pollutant formation.

Other methods for reducing the formation of dust in the gasification of whole bales of chunky or stacked lumpy biomass are not known. Object of the invention

The present invention has for its object to provide a very easy to implement method with appropriate device for reducing dust emissions in the thermal gasification of biomass, in particular of whole bales of halmartiger biomass from the field and from lumpy wood in which the formation of liquid Slag and fine dust is lowered at the place of gas formation. The resulting amounts of liquid slag and fine dust should be retained as possible in the gasifier room.

Another task is the inclusion of a gas scrubbing in the exhaust gas purification of gasification plants also small power to remove the residual amounts of fine dust, slag and pollutants without contaminated wastewater must be treated and disposed of.

According to the invention the object is achieved according to the features of claim one.

Accordingly, to reduce the particulate matter in the fuel gas and exhaust gas in the thermal gasification of chunky or lumpy biomass in the form of bales, bundles, stacks or pellets, in which the gasification by heating by combustion of a proportion of biomass in the gasifier chamber (2) and that generated Fuel gas burned outside the gasifier chamber (2) and passed through a heat exchanger (18), carried out the following method steps:

In the gasifier chamber (2, 14) after the beginning of the gasification metered water or water vapor as a function of room temperature in the gasifier chamber (2, 14) introduced to a room temperature of 280 to 650 ⁰ C, or 450 to 800 ⁰ C in To ensure bales (1). As a result, only small amounts of ash are melted and fine dust is formed.

- The ratio of the volume of the biomass charge (1, 15) in the gasifier chamber (2, 14) for heat output of the fuel gas produced per hour is at least 0.005 m ³ per KW, so that the gasification volume per m ³ biomass charge (1, 15) and thus the gassing rate is kept low.

The fuel gas produced is burned immediately, without intermediate cooling, in a combustion chamber (6) at temperatures above 720 ⁰ C.

It has surprisingly been found that an addition of water or water vapor also brings about an improvement in gasification in the gasification of hemi-biomass in bales and lumpy biomass in the stack, although in this case the temperature is lowered.

Water vapor has about twice as high specific heat capacity as the gas mixture initially present there, which consists in particular of nitrogen, oxygen, carbon dioxide, carbon monoxide and other cracking products. This allows water vapor at the same temperature a much higher amount of heat transferred to the biomass, as the other gases assets. The halm-like or lumpy biomass in bales or stacks always burns or gasses unevenly, because there are only a few burns or embers in the total mass that "move" through the biomass, where the temperature is highest, in more distant layers In the immediate vicinity of oxidation reactions, the splitting of the water releases hydrogen (H ₂ ), whose thermal conductivity is about 8 times higher than the other gases mentioned above, so that hydrogen is also able to make a contribution that heat is distributed more evenly on the biomass and on whose surface temperatures rise.

The water entry into the gasifier space thus causes a total of more gasification takes place by an increased heat transfer to the biomass at the same or lower temperature. This effect is known through the hot air sauna. If in the sweat room with near 100 ⁰ C water is given to the heater, creates a cloud of steam, which is only a few degrees warmer than the sauna air, but is perceived as much hotter. The human body then absorbs a lot more heat energy for a while and so does the biomass in the gasifier room. There, the gasification is intensified and more biomass is turned into gas. Thereupon, the control of the carburetor with a reduction in the combustion air supply, the heat of combustion released becomes lower and so decrease the temperatures in the carburetor.

The steam takes up heat where the combustion takes place particularly strongly at certain points, thus ensuring a much more uniform temperature and energy distribution in the gasifier chamber. As a result of this, a much larger amount of the biomass present in the gasification space is involved in the gasification processes. As a result, pyrolysis and gasification can take place much more slowly at certain points. The gasification rate as a gas amount relative to the total biomass present in the gasification chamber thus becomes considerably smaller. As a result, less molten mineral is entrained in the microstructure of the biomass at the gas outlet. As a result, the formation of fine dust is reduced.

The average temperature level in the carburetor room drops and so many mineral components are no longer melted. The undesired local Tempe ^¬ raturspitzen, where the combustion takes place to be broken and so the evaporation low melt ^¬ of the salts can be largely prevented. The desired amount of gas can thus be generated in the presence of water vapor at a lower, medium temperature. It is less of the low-melting salts and oxides from the ash or just planted in gasification plant part melted, torn into the gas stream or to a lesser extent already evaporated. The gasification is much more uniform over the large amount of biomass distributed over a period of many hours, as a very slow and less eruptive process. As a result, the melted material and particulate matter adhere to non-melting ash constituents and the moist biomass structure in the gasifier chamber, so it does not enter the gas flow and this removes only a fraction of the previous amount of mineral dust.

By far the largest amount of particulate matter forming in the ash remains in the gas chambers in the ash compartments, and so the dust content in the exhaust gas drops to a surprisingly high degree to only a fraction of the previous value.

It is the low-melting salts and oxides that combine with simple ones. Cyclones or settling spaces produce hardly detectable particulate matter. The melting points of the occurring in the following Ascheinhaltsstoffe are substantially in the range of 160-650 ⁰ C:

Aluminum chloride, nitrate, sulphate,

Ammonium nitrate, sulfate, iron sulfate

Ferrous chloride

Potassium chlorate, sulphate, sulphide, nitrate, oxide

Sodium chlorate, metaphosphate, nitrite, phosphate

calcium nitrate

Magnesium oxide, sulfate, chloride,

Copper chloride, sulfate

Manganese oxide, chloride

Phosphorus oxide, sulfide (Cold oven, Chemistry, Harri Deutsch)

Cereal straw is very rich in alkali compounds, especially those of potassium and these are mainly composed of white particulate matter. First to mention is the potassium oxide. The exact composition of ashes in the biomass is different in the different energy plants and also very soil-related.

The subsequent combustion immediately after gasification without intermediate cooling of the fuel gas at temperatures above 750 ° C cause safe disposal of environmentally harmful chemical compounds that may arise in the gasification at low temperatures.

By using the method, the heat exchanger surfaces arranged after the combustion chamber remain clean much longer and cleaning is rarely required.

According to the invention the object is achieved in a second variant according to the features of claim two. Accordingly, to reduce the particulate matter in the exhaust gas in the thermal gasification of chunky or lumpy biomass in the form of bales, bundles, stacks or pellets and subsequent combustion of the fuel gas, the gasification by heating by combustion of a proportion of biomass in the gasifier chamber (2, 14 ) and that the fuel gas produced is burned outside the gasifier chamber (2, 14) and passed through a heat exchanger (18), the following method steps are carried out:

- The exhaust gas is then passed through a Quenchraum (26) to precipitate the slag and dust particles.

In the gasifier chamber (2, 14) is metered after the beginning of the gasification, charged water from the quenching chamber (26) as a function of the room temperature in the gasifier chamber (2, 14) to a room temperature of 280 to

650 ⁰ C or 450 to 800 ⁰ C in the bale (1) to ensure.

Thus, the water is evaporated and the solids and the resulting particulate matter and the slag are in the

Biomass charge predominantly held and the with the

Fuel gas discharged directly, without

Intermediate cooling in a combustion chamber (6) burned at temperatures above 720 ⁰ C.

This procedure also allows for small

Carburetor boilers for biomass good exhaust gas cleaning without having to treat treated wastewater or dispose of it specially.

Both methods according to claim 1 and 2 can also be combined with each other.

According to a preferred embodiment of claim 3, the total introduction of water into the bale case space is made from stalks in an amount of 3 to 35%, in particular 20%, based on the total weight of whole bales.

It has been found that by introducing water into the gasifier space of a whole-body gasifier in an amount of about 20% by weight of gasified biomass (naturally dried straw) per unit time, a reduction of particulate matter emission from previously more than 90mg / standard cubic meter of exhaust gas to about 20mg / standard cubic meter enters. This complies with the applicable exhaust emission limits and can be dispensed with the installation of a costly particulate matter filter. It has been shown that the fine dust-reducing effect of adding water to the gasification already moved in about 3% is easily measured by weight per unit time deflagrating biomass, but 35% should not be exceeded because then hardly any water in the Konvertie ^¬ approximately responsive (CO + H2O-H2 + CO2) can be implemented. Then Water vapor increasingly enters the product gas and affects the calorific value of the gas. The optimum water addition is in the range of 5% to 15%, based on the total mass. The water can be introduced in any state of aggregation and at any temperature in the gasifier chamber. Of course, the use of normal tap water is easiest.

The dependent claims 4 to 7 contain process steps for optimal introduction of water, sewage or steam in the Vergaserräum.

The subclaims 8 and 9 contain preferred control methods for the metering of water, waste water or steam and the amount of circulated air blown on the biomass in the gasification chamber.

Claims 10 to 13 relate to preferred embodiments of the devices for carrying out the method.

Examples

The method and the device will be explained below with two examples.

The figure I shows a straw all-ball carburetor in the cross section from the front, the Fig. II the same straw Ganzball carburetor in a side view in section and Fig. III a Holzvergaserkessels smaller power in cross-section from the front. example 1

According to FIG. 1, a cylindrical bale 1 of straw lies in the gasifier chamber 2. This bale is provided with a ceramic lining 3. The bale 1 lies on a combustion grate 4. Darun- ter is the fuel gas exhaust opening 5, which opens into the combustion chamber 6, not shown. In the lower part of the carburetor 2 ashes 7 are arranged on both sides.

The combustion air is sucked through the channel for the air supply 8 and into this projecting into the water Einsprit zeinrichtung 9. This consists of warm - and corrosion-resistant material and contains a cross-sectional constriction. The pipe 13 carries the water to the water injection device 9 via a filter 10, not shown, an adjustable pressure reducer 11 and the solenoid valve 12th

In operation, the water is thus injected from the top of the side of the bales in gasification 1, it evaporates, the existing gas mixture in the gasifier chamber 2 is enriched with water vapor, this is overheated and then transfers more heat energy at a lower temperature to the biomass. Not shown is a known heat exchanger 18, which is arranged downstream of the combustion chamber 6. In this, the hot gas releases the heat to a water cycle. If, after this, a known quenching chamber is arranged for separating the remaining particulate matter, the resulting contaminated water is injected via the pipeline 13 and the water injection device 9 into the air supply 8. In this variant, the filter 10, pressure reducer 11 and the solenoid valve 12 omitted. For the supply a controllable pump is used.

Example 2

With Fig. III, a further embodiment will be explained.

This is the cross-section of a wood gasification boiler of smaller power, with very coarse firewood is filled for a gasification and burning time of at least 7 hours.

In the carburetor chamber 14 for stack are coarse firewood pieces 15. Again, the carburetor chamber 14 has a ceramic lining 16 for heat insulation. Thus, the heat is largely retained for the gasification and the conversion reaction. The combustion air is supplied from both sides of the gasifier chamber 14 through the air channels 17 to the fuel wood pieces 15 to be gasified. The generated gas is drawn down into the combustion chamber 6, not shown.

Into the carburetor chamber 14 projects from above a feed tube 19 into which a small funnel 20 is inserted. In this drips water from the dripper 21. The water is supplied via the water line 25 through the adjustable pressure reducing device 23, the valve 24 and the water filter 22. By the dripper 21 small amounts of water can be dosed better constipation than with a then too fine water jet. With the easily adjustable number of drops of water per unit of time, the water additive can be dosed and optically controlled.

For a wood gasifier boiler with 20 kW heating capacity, it is recommended to add about one liter of water per burning hour. That's about 100 drops of cold water per minute.

List of reference numbers

Bales from stalks Carburetor room (for bales) Ceramic lining Stove Grate gas vent combustion chamber Ashtrays Channel for air supply Water injector Filter Pressure reducer Solenoid valve Pipeline Carburetor room (for stacks) Firewood pieces Ceramic lining Air ducts Heat exchanger Feed tube Funnel Drip device Water filter Pressure reducer Valve Water line Quenching chamber

Claims

claims

1. A method for reducing the particulate matter in the exhaust gas in the thermal gasification of chunky or lumpy biomass in the form of bales, bundles, stacks or pellets and subsequent combustion of the fuel gas, the gasification by heating by combustion of a proportion of biomass in the gasifier chamber (2) takes place and that fuel gas produced is burned outside the gasifier chamber (2) and passed through a heat exchanger (18), characterized in that in the gasifier chamber (2, 14) after the beginning of the

Gasification metered water or steam as a function of the room temperature in the gasifier chamber (2, 14) is introduced to a room temperature of 280 to 650 ° C, or 450 to 800

⁰ C in the bale (1) to ensure that only small amounts of ash are melted and fine dust are formed and the ratio of the volume of biomass charge (1, 15) in the

Carburetor space (2, 14) for heat output of the generated

Fuel gas per hour is at least 0.005 m ³ per KW, so that the gasification volume per m ³ biomass charge (1, 15) and thus the gassing is kept low and the fuel gas produced directly, without intermediate cooling in a combustion chamber (6) at temperatures above 750 ⁰ C is burned.

2. A method for reducing the particulate matter in the exhaust gas in the thermal gasification of chunky or lumpy biomass in the form of bales, bundles, stacks or pellets and subsequent combustion of the fuel gas, wherein the Gasification by heating by combustion of a portion of the biomass in the gasifier chamber (2, 14) takes place and that fuel gas produced outside the gasifier chamber (2, 14) is burned and passed through a heat exchanger (18), characterized in that the fuel gas is then passed through a quench (26) is passed to precipitate the slag and dust components that metered into the gasifier chamber (2, 14) after the start of gasification, charged water from the quench (26) depending on the room temperature in the carburetor chamber (2, 14) introduced is to ensure a room temperature of 280 to 650 ⁰ C and 450 to 800 ⁰ C in the bale (1), so that the water evaporates and the solids and the resulting particulate matter and slag in the Biomassecharge predominantly recorded and with the Fuel gas discharged portion directly, without intermediate cooling in a combustion chamber (6) is burned at temperatures above 720 ⁰ C.

3. The method according to claim 1, characterized in that the total entry of water in the carburetor space for whole bales of stalks in an amount of 3 to 35%, in particular by 20%, based on the total weight of whole bales is performed.

4. The method according to claim 2, characterized in that in the quenching chamber (26) sprayed water is collected below this and metered into the gasifier chamber (2, 14) is introduced.

5. The method according to any one of claims 1 to 4, characterized in that the water or steam additive in the gasifier chamber (2, 14) evenly distributed, spatially far from the fuel gas discharge opening (5) takes place.

6. The method according to any one of claims 1 to 4, characterized in that water is sprayed into the channel for the air supply (8) of the combustion air.

7. The method according to any one of claims 1 to 4, characterized in that water is dripped or sprayed above the biomass lying in the gasifier chamber (2, 14).

8. The method according to any one of claims 1 to 7, characterized in that the temperature in the gasifier chamber (2, 14) measured and the standard amount of water or Dampfzugäbe per kg. Biomass and time unit is increased linearly with increasing temperature from 400 ⁰ C, so that 650 ⁰ C in the gasifier chamber (2, 14) are not exceeded.

9. The method according to any one of claims 1 to 8, characterized in that in the gasifier chamber (2, 14) as known, taken gas and concentrated locally on the biomass in the form of bales (l), bundles, stacks (15) or pellets and accelerated is blown to remove slag and ash, the temperature measured in the gasifier room and the standard amount of gas blowing per kg. Biomass and time unit at

Temperatures below 400 ⁰ C are increased linearly to a minimum amount of water metering in the gasifier compartment

(2, 14).

10. Apparatus for carrying out the method according to claim 1, consisting of a carburetor space (2) for the limb-shaped biomass in the form of bales (1), arranged in the upper region channel for the air supply (8) of the combustion air, arranged in the lower region Grate (4) with fuel gas exhaust opening (5) and adjoining combustion chamber (6), characterized that approximately centrally in the channel for the air supply (8) a water injection device (9) is attached, via a pipe (13) with a filter (10), pressure reducer (11) and solenoid valve (12) with the water line (25) or directly connected with a pump to the tank for quench water.

11. Apparatus for carrying out the method according to claim

1, consisting of a carburetor space (14) for the biomass in the form of firewood stacks (15), firewood bundles or a pellet bed, arranged in the central region air channels (17) for supplying the combustion air, arranged in the lower region fuel gas exhaust opening (5) and thereto subsequent combustion chamber (6), characterized in that at the top of the filling and carburetor chamber (14), approximately centrally, a feed tube (19) with funnel (20) and above a drip device (21) is arranged, which via a pipe with a water filter (22), pressure reducing device (23) and valve (24) to the water line (25) or the feed pipe (19) is connected directly to a pump to the tank for quench water.

12. Apparatus for carrying out the method according to claim

2, consisting of a fuel gas outlet opening (5) for the biomass, air ducts (17) for the supply of combustion air, arranged in the lower region fuel gas discharge opening (5) and adjoining combustion chamber

(6), and heat exchanger (18), characterized in that the heat exchanger is connected downstream with a Quenchraum (26) having a Quenchwassersammelraum in the lower region, a sewer pipe with metering pump, which connects to the upper carburetor space (2) and a regulation for the dosing pump with a temperature sensor in the gasifier chamber (14) regulates the pump output.

13. Device according to one of claims 10 to 12, characterized in that a programmable logic controller with input side

Temperature sensors in the carburetor chamber (2, 14) and in the heated

Water or steam room of the heat exchanger and the output side with the water metering with

Pressure reducing device (23) and valve (24) or

Dosing pump, and blower in the gasifier chamber (2, 14) is connected, a selectable data memory for the specific

Dosing quantities of water and air blow per kg. Biomass sort and

Time unit exists, so that a basic setting and a subsequent regulation to comply with the limits of

Temperatures and water additions are allowed.