DE10227074A1 - Process for gasifying biomass and plant therefor - Google Patents

Abstract

A method for the gasification of biomass (B) in a gasification reactor (2) by thermo-chemical decomposition of hydrocarbons in a water vapor atmosphere has the steps: DOLLAR A - combustion of substances in a combustion chamber (3) separated from the gasification reactor (2) in a gas-tight manner, DOLLAR A - supply of thermal energy from the combustion chamber (3) into the gasification reactor (2), and DOLLAR A - discharge of the combustion gases (A) from the combustion chamber (3) separately from the product gases generated during the gasification of the biomass (B) (P ).

Description

The invention relates to a method for the gasification of biomass in a gasification reactor by thermo-chemical Decomposition of hydrocarbons in a water vapor atmosphere.

The invention further relates to a plant for the gasification of biomass with a gasification reactor, the for the thermo-chemical decomposition of hydrocarbons in a water vapor atmosphere is formed, and with a combustion chamber for exothermic Burning substances, preferably oxidizing gases, however possibly also from liquid or solid substances with atmospheric oxygen.

In view of the future reduction in quantities available There is a need for fossil fuels, fuel through synthesis to generate from biomass. For example, forest wood, Reeds, corn, straw or other biomass can be used. The Synthesis takes place with a coupling of thermolysis, reactolysis, Fischer-Tropsch synthesis and refining processes. This synthetic process have to however adapted to the conditions of the starting material, to the final product adjusted and combined in a special way.

The aim of the synthesis of biomass is to obtain aliphatic hydrocarbons (CH ₍₂₎ ) _nalKW , which can be refined and used as fuel or mixed with conventional fossil fuels.

There are biological processes for this for the implementation of biomass, such as B. methane fermentation or alcoholic fermentation, known where primary Methane and secondary Methanol or ethanol can be produced. The biological process are only for selected Biomass compositions can be used and on the special composition of biomass restricted. The speed of the biological processes is also optimal Temperature range relatively low, making it an industrial scale Application of biological methods is hardly possible.

There are also thermo-chemical thermolysis processes known, however, the use of the products of such thermolysis (Pyrolysis) severely restricted is because the thermolysis oil produced is a very heterogeneous composition owns and not directly for refining is suitable. These problems can only be partially overcome the so-called flash pyrolysis can be solved. In particular complicate inorganic components in the thermolysis oil the further treatment, whereby cleaning the in liquid Phase of the present thermolysis oil is more difficult than cleaning a gas phase.

There are also thermo-chemical reactolysis processes known with which gaseous Products are created. In the generated reactolysis gases are in usually accompanying substances that prevent a direct synthesis. However, are for Almost all accompanying substances cleaning processes known. Under the The term reactolysis is used in the following as a direct thermo-chemical Decomposition of the biomass by gasification of the biomass in water vapor the atmosphere Roger that.

The thermo-chemical thermolysis process have so far been used as a precursor for reactolysis processes.

Synthetic processes for the production of aliphatic hydrocarbons (CH ₍₂₎ ) are also _known from a mixture of carbon monoxide CO and hydrogen H ₂ . In the so-called Fischer-Tropsch synthesis, aliphatic hydrocarbons (CH ₍₂₎ ) are _used according to the equation n (CO + 2 H ₂ ) = n H ₂ O + (CH ₍₂₎ ) _nalKW generated from a synthesis gas as a mixture of carbon monoxide CO and hydrogen H ₂ .

The synthesis gas can be generated from biomass by thermo-chemical conversion. For example, a direct thermo-chemical decomposition of the biomass with water vapor can be used according to the so-called reactolysis process in order to generate the synthesis gas as a mixture of carbon monoxide CO and hydrogen H ₂ . The following relationship applies: (CH ₍₂₎ ) _{n biomass} + n H ₂ O = n (CO + 2 H ₂ ) ,

The endothermic process of thermo-chemical decomposition requires thermal support through an exothermic reaction, which can take place through internal combustion with oxygen or via an external energy supply. In the case of internal combustion, it is disadvantageous that the proportions of the gases required for the synthesis (carbon monoxide CO and hydrogen H ₂ ) are shifted absolutely and visibly in a relatively unfavorable manner with regard to their stoichiometric ratio. In addition, carbon atoms in the biomass leave the balance as carbon dioxide CO ₂ and thus reduce the amount of hydrocarbons that can be synthesized.

The synthesis of aliphatic hydrocarbons ((CH _{(2)) nalKW} from the gases carbon monoxide CO and hydrogen H _2, however, is under the given conditions exothermic. The synthesis requires indeed a catalytic guide, but no thermal support, since the reaction to water, H ₂ O releases more energy than the coupled synthesis of hydrocarbons requires.

Fixed bed gasifiers, entrained flow gasifiers and fluidized bed gasifiers are known for the gasification of biomass in the reactolysis process. Fixed bed countercurrent gasifiers have a very high tar content in the product gas, which makes aftertreatment extremely difficult. With fixed bed direct current ver Gasers, on the other hand, only produce small amounts of tar. Fixed bed gasifiers have the disadvantage that stable beds have to be formed, so that the biomass has to be reliably pelleted.

With entrained-flow gasification takes place first with Pre-gasification preconditioning biomass in Lean gas, coke and oil. Subsequently there is gasification in the entrained flow at high temperatures in the upper Area of the reactor with oxygen. One is then in the same reactor Reduction of the gases at about 650 to 800 ° C in the lower area of the reactor carried out with steam. The entrained flow gasifiers are due to the required two reactors relatively expensive and have a limited efficiency.

With conventional eddy current gasification biomass is gasified in a fluidized bed system with air as a gasifying agent. The fluidized bed gasifiers have one Gasification zone which is swirled with steam and a combustion zone, which is swirled with air. In the combustion zone there is charcoal burned and thus generates the necessary thermal energy for gasification. The circulating bed material transports the heat from the combustion zone to the gasification zone. The problem is to prevent that the exhaust gases from the combustion zone do not mix with the product gas if possible mix and contaminate it.

Another embodiment of fluidized bed gasifiers use water vapor as a gasifying agent to the so-called Battelle process or FICFB process (Fast-Internally-Cirulating-Fluidized-Bed). at In both steam gasification processes, the heat is circulated through a bed material fed in an allothermal process. Over two-bed fluidized beds gasification takes place with steam and combustion with air.

Based on this, it is task of the invention, an improved method for gasifying biomass as well as to create a plant for this, with the biomass of different Origin of synthesizable product gases, especially for further processing for economical use as fuel.

• – Verbrennung von Substanzen, beispielsweise von Oxidationsgasen, in einer von dem Vergasungsreaktor gasdicht getrennten Verbrennungskammer,
• – Zuführen von Wärmeenergie aus der Verbrennungskammer in den Vergasungsreaktor, und
• – Ableiten der Verbrennungsgase aus der Verbrennungskammer getrennt von den bei der Vergasung der Biomasse erzeugten Produktgasen.

The object is achieved with the generic method according to the invention by:

• Combustion of substances, for example oxidation gases, in a combustion chamber separated from the gasification reactor in a gastight manner,
• - supplying thermal energy from the combustion chamber into the gasification reactor, and
• - Deriving the combustion gases from the combustion chamber separately from the product gases generated during the gasification of the biomass.

In contrast to the conventional ones Process is now proposed, the combustion of oxidizing gases as an exothermic process for the thermal support of the endothermic process the decomposition of hydrocarbons gas-tight separately from the Process of decomposition in the gasification reactor and only the thermal energy to pass from the combustion chamber into the gasification reactor. there the combustion gases are then separated from that in the gasification reactor generated product gases dissipated.

This procedure has the advantage that a production of product gases with high purity on energetic economic way with relatively little investment in the facility is made possible.

The exothermic process of combustion the oxidation gases are preferably produced by product gases from the gasification reactor entertain that are introduced as oxidation gases into the combustion chamber become. The process can initially be carried out by externally supplied oxidation gases be initiated and subsequently the proportion of product gases in the oxidation gases can be increased.

In the combustion chamber is preferred a mixture of air, natural gas and product gas as the oxidizing gas directed and burned there. The reactor process in the gasification reactor preferably carried out in a hydrogen-containing atmosphere a gas mixture of oxygen, water vapor and natural gas as the reactolysis gas having.

It is particularly advantageous if the process of gasification in an eddy current gasification reactor carried out becomes. This has been compared to fixed bed and entrained flow gasifiers proven to be economically and technically advantageous.

Before gasifying the biomass should conditioning of the biomass, for example by mechanical Shredding can be done. So that the energy balance of the Procedure to be improved.

By gasifying the biomass generated product gases are then preferably cleaned and synthesized for example by the Fischer-Tropsch synthesis process. The gasification the biomass is preferably controlled by supplying oxygen. It is also particularly advantageous if the biomass is in a fluidized bed gasified with additives such as sand, aluminum oxide and / or dolomite or the like becomes. Through a process can the residual solids arising from the gasification reactor during gasification be removed. After sieving off the residual solids, the sieved aggregates, especially sand, again as aggregates fed to the gasification reactor become.

The object is further achieved by the generic system according to the invention in that that the gasification reactor is arranged in a gas-tight manner from the combustion chamber in such a way that thermal energy is conducted from the combustion chamber into the gasification reactor and the combustion gases are derived from the combustion chamber separately from the product gases generated during the gasification of the biomass.

It is particularly advantageous if the product gas is passed through a centrifugal separator for cleaning becomes.

The invention is described below the attached Drawing closer explained. It shows:

1 Sectional view of a plant according to the invention for gasifying biomass.

The 1 leaves a system according to the invention 1 to gasify biomass, which is essentially a gasification reactor 2 for the thermo-chemical decomposition of hydrocarbons in a water vapor atmosphere and a combustion chamber separated from them in a gastight manner 3 for the combustion of oxidation gases G. The exothermic process of combustion of oxidizing gases G in the combustion chamber 3 is thus spatially separated from the reactolysis, ie the thermo-chemical decomposition, in the gasification reactor 2 performed gastight. The endothermic process of reactolysis in the gasification reactor 2 is due to the exothermic process in the combustion chamber 3 to chat. This is the gasification reactor 2 in the combustion chamber 3 added, the outer wall of the gasification reactor 2 the inner wall of the combustion chamber 3 forms. The heat exchange from the combustion chamber 3 to the gasification reactor 2 thus takes place via the outer wall 4 of the gasification reactor 2 , In this way, a complete separation of the in the gasification reactor is constructively 2 generated product gases P from the reductive phase of those in the combustion chamber 3 generated gases from the oxidative phase.

The exothermic process in the combustion chamber 3 is maintained by the oxidizing gases G via a supply line 5 in the upper area into the combustion chamber 3 be directed. A mixture of atmospheric oxygen L, product gas P and natural gas E is burned as oxidation gases G, which are mixed in a controlled ratio. At the beginning of the gasification of biomass B, the combustion process is obtained by atmospheric oxygen L and natural gas E.

Later the proportion of product gas P keeps increasing and in particular the proportion of natural gas E is reduced.

That with the combustion in the combustion chamber 3 resulting combustion gas A is through an exhaust outlet 9 in the lower part of the combustion chamber 3 derived.

The one in the combustion chamber 3 recorded gasification reactor 2 has a fluidized bed grate inclined relative to the horizontal plane in the lower area 10 with gas passage openings. At least one feed line opens below the fluidized bed grate 11 for reactor lysis gases R to maintain the thermo-chemical decomposition in the gasification reactor 2 , The reactolysis gases R are preferably a mixture of oxygen O, hydrogen H ₂ and natural gas E. The biomass B is preferably mixed with additives Z, such as, for. B. sand, aluminum oxide, dolomite etc. via a funnel 12 with feed into the gasification reactor 2 directed. Via an exhaust air duct 13 in the upper area of the gasification reactor 2 the product gas P generated during the reactolysis is derived and by a centrifugal separator (cyclone) 14 led to cleaning. Part of the purified product gas P can be via a product gas line 15 back into the gasification reactor 2 be returned directly.

The gasification reactor 2 is operated at temperatures of around 500 to 900 ° C in a reducing hydrogen atmosphere largely in the absence of air, so that thermo-chemical decomposition of the hydrocarbons is ensured. The gas temperature in the outer combustion chamber 3 is about 800 to 1200 ° C, the combustion takes place in an oxidative atmosphere. It is essential to the invention that the exhaust gases A generated during the combustion are derived separately from the product gases P by the combustion chamber 3 gas-tight from the gasification reactor 2 is. The endothermic process of gasification is accomplished by heat exchange from the combustion reactor 3 over the outer wall 4 in the gasification reactor 2 to chat.

The residual solids from gasification are discharged into a sieve 16 dissipated. Additives Z, in particular sand, can be sieved out and over the filling funnel 12 be returned to the gasification process. The remaining fabrics 17 however, are discarded.

The gasification process is preferably controlled initially autothermally with the addition of oxygen. The biomass B should also be gasified in such a way that an almost ideal product gas mixture P of carbon monoxide CO and hydrogen H _{2 is obtained} in a molar ratio of about 1 to 2. The generated product gases P are after dedusting in the centrifugal separator 14 further processed. This post-processing process, not shown, can cool the product gases 9 via heat exchangers and a downstream fine dedusting system. In addition, an alternately switchable tar catalyst can be provided as a safety level if, for. B. the tar content increases inadmissibly during load changes. Possibly separated tar is burned off oxidatively by means of this alternating circuit. Removal of sulfur H ₂ S and halides, e.g. B. HCl, with laundry can join. In addition, a shift stage and carbon dioxide washing can be provided.

After cleaning the product gases 9 a known synthesis takes place, for example, according to the Fischer-Tropsch process. The desired boiling cuts can be obtained from the resulting aliphatic hydrocarbons, such as in conventional gasoline and diesel production with the help of catalysts. The primary oil produced during the synthesis can later be refined, whereby the fuels are obtained from the corresponding boiling cuts and blended.

Claims (20)

Process for gasifying biomass (B) in a gasification reactor ( 2 ) by thermo-chemical decomposition of hydrocarbons in a water vapor atmosphere, characterized by - combustion of substances in one of the gasification reactor ( 2 ) gas-tight separate combustion chamber ( 3 ), - supplying thermal energy from the combustion chamber ( 3 ) in the gasification reactor ( 2 ), and - deriving the combustion gases (A) from the combustion chamber ( 3 ) separately from the product gases (P) generated during the gasification of the biomass (B). A method according to claim 1, characterized in that the Substances Oxidation gases (G), liquid and / or solid substances that are burned with atmospheric oxygen. A method according to claim 1 or 2, characterized by introducing product gases (P) as oxidation gases (G) into the combustion chamber ( 3 ). Method according to one of claims 1 to 3, characterized by gasification in an eddy current gasification reactor. Method according to one of the preceding claims, characterized characterized in that before the gasification of the biomass (B) a conditioning of the Biomass (B) takes place. Method according to one of the preceding claims, characterized by controlling the gasification of the biomass (B) by supplying Oxygen (O). Method according to one of the preceding claims, characterized by gasifying the biomass (B) in a fluidized bed, taking aggregates (Z), such as sand, aluminum oxide and / or dolomite in the fluidized bed be introduced. Method according to one of the preceding claims, characterized by supplying a mixture of air (L), natural gas (E) and product gas (P) as the oxidizing gas (G) into the combustion chamber ( 3 ). Method according to one of the preceding claims, characterized by supplying water vapor (H ₂ ) and optimally a gas mixture of oxygen (O) and natural gas (E) as the reactolysis gas (R) into the gasification reactor ( 2 ). Investment ( 1 ) for the gasification of biomass (B) with a gasification reactor ( 2 ), which is designed for the thermo-chemical decomposition of hydrocarbons in a water vapor atmosphere, and with a combustion chamber ( 3 ) for the combustion of substances, for example oxidation gases (G), characterized in that the gasification reactor ( 2 ) gas-tight from the combustion chamber ( 3 ) is arranged separately so that thermal energy from the combustion chamber ( 3 ) in the gasification reactor ( 2 ) and the combustion gases (A) from the combustion chamber ( 3 ) are derived separately from the product gases (P) generated during the gasification of the biomass (B). Investment ( 1 ) according to claim 10, characterized in that the gasification reactor ( 2 ) is an eddy current gasification reactor. Investment ( 1 ) according to claim 10 or 11, characterized in that the gasification reactor ( 2 ) in the combustion chamber ( 3 ) and the combustion chamber ( 3 ) through the outer wall ( 4 ) of the gasification reactor ( 2 ) is limited. Investment ( 1 ) according to one of claims 10 to 12, characterized by at least one supply line ( 5 ) for oxidation gases (G) in the upper area, preferably in the lid of the combustion chamber ( 3 ). Investment ( 1 ) according to claim 13, characterized in that means for mixing oxidizing gas (G) from air (L), product gas (P) and natural gas (E) are connected in a controlled ratio to the at least one supply line. Investment ( 1 ) according to one of claims 10 to 14, characterized by a combustion gas outlet ( 9 ) in the lower part of the combustion chamber ( 3 ). Investment ( 1 ) according to one of claims 10 to 15, characterized by a fluidized bed grating inclined to a horizontal plane ( 10 ) with gas passage openings in the gasification reactor ( 2 ), below the fluidized bed grate ( 10 ) at least one supply line ( 11 ) for reactolysis gases (R) for thermo-chemical decomposition in the gasification reactor ( 2 ) flows out. Investment ( 1 ) according to claim 16, characterized by means for mixing reactolysis gas (R) in a controlled ratio of at least oxygen (O), hydrogen (H ₂ ) and natural gas (E). Investment ( 1 ) according to one of claims 16 or 17, characterized by an outlet for removing residual solids resulting from the gasification, the outlet from the fluidized bed grate ( 10 ) from the gasification reactor ( 2 ) and through the combustion chamber ( 3 ) out of the system ( 1 ) runs out. Investment ( 1 ) according to claim 10, characterized by a sieve connected to the outlet ( 16 ) for sieving out aggregates (Z) from the residual solids, the aggregates (Z) again in the gasification reactor ( 2 ) are introduced. Investment ( 1 ) according to one of claims 16 to 19, characterized in that the product gas (P) by a centrifugal separator ( 14 ) is conducted.