BG111209A - Method for producing electrical and thermal energy from biomass - Google Patents

Abstract

The method provides the energy conversion of biomass into electrical and thermal energy and waste product as bio-coal. The method comprises a continuous process in which the comminuted and partially dried biomass material is fed in oxidation-reduction chamber, provided with a burner, where it is heated by direct contact of the biomass with the flue gases generated by the burner, under conditions of oxidizing atmosphere in the upper zone of the combustion chamber and reduction atmosphere in the remaining part of the chamber. At a temperature in the chamber between 150 ° C and 400 C, partial pyrolysis of biomass is carried out and contained moisture, volatiles and gaseous products resulting from the partial pyrolysis are released and passed in flue gases, and the resulting charred solid material is a waste product in the form of bio-coal on the type of wood charcoal with calorific value similar to that of brown coal, and is discharged from the combustion chamber. The flue gases containing the released from the biomass moisture, volatiles and gaseous products of the partial pyrolysis are discharged from the oxidation-reduction chamber and are fed in a chamber for reburning, equipped with burners, wherein is carried out the complete combustion of the gases and containing in them hydrocarbons for obtaining of additional amount of thermal energy. After removal from the reburning chamber the flue gases are fed to the high temperature heat exchanger, wherein heat a flow of recirculation flue gases, fed back into the oxidation-reduction chamber. After the high temperature heat exchanger the flue gases pass through a second heat exchanger connected to a cycle for producing of electrical and thermal energy, wherein the flow of flue gases heats an agent used in the cycle.

Description

The invention relates to a method for producing electricity and heat from biomass by a combined circular process using an Organic Rankin cycle or other conventional cycle to generate electricity and heat, and in particular to a conversion process of biomass in electricity and heat and waste in the form of charcoal-like bio-coal with a calorific value close to that of brown coal.

BACKGROUND OF THE INVENTION

US 2009/0260286 discloses a method of producing electrical and thermal energy from biomass by a continuous process involving the pyrolysis of biomass in a rotary kiln by indirectly heating the biomass in the absence of oxygen to produce pyrolysis gas and charcoal fed into a gasifier, where gasification of particulate matter and charcoal in the presence of oxygen takes place. The generated exhaust gas is passed through particulate filters, then fed to a heat exchanger that is used to heat water for various purposes, and the exhaust gas passed through the heat exchanger is fed to an electricity generator.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for producing electricity and heat from biomass, which provides higher process efficiency by using small amounts of additional fuel.

This task is solved by a method for producing electrical and thermal energy from biomass by a continuous process in which the crushed and partially dried biomass material is fed into a redox chamber equipped with a burner where it is heated by direct contact of the biomass with the fumes gases generated by the burner under oxidation conditions in the upper zone of the combustion chamber and reduction in the rest of the chamber. At a temperature in the chamber between 150 ° C and 400 ° C, partial pyrolysis of the biomass takes place and the moisture, volatiles and gaseous products resulting from the partial pyrolysis are separated and passed into the flue gases, and the resulting charred solid • ·

the material is a waste product in the form of charcoal of a type of charcoal with a calorific value close to that of brown coal, and is unloaded from the combustion chamber. The flue gases containing moisture, volatile matter and gaseous products of partial pyrolysis separated from the biomass are removed from the redox chamber and fed into a combustion chamber equipped with burners, where complete combustion of the gases and the hydrocarbons contained therein takes place to produce them. extra amount of heat. After removal from the combustion chamber, the flue gases are fed to a high temperature heat exchanger, where they heat a stream of recirculating flue gases fed back into the redox chamber. After the high-temperature heat exchanger, the flue gases pass through a second heat exchanger connected to a cycle for the generation of electrical and thermal energy, where the flue gas stream heats the agent used in the cycle. The flow of flue gases leaving the second heat exchanger is divided into two streams, one of them being said flow of recirculating flue gases, which, after separation of the moisture contained therein, is fed to the high-temperature pre-heating heat exchanger, and then feeds back into the redox chamber. The other flue gas stream is used to partially dry the biomass feedstock before being fed into the redox chamber.

The oxidation atmosphere in the upper part of the redox chamber, in which partial pyrolysis of the biomass is carried out, has an excess of oxygen of up to 10%.

It is preferable for the redox chamber to operate under pressure conditions in the range of 80 to 100 kPa (abs).

In one embodiment of the invention, the redox chamber is a cylindrical rotary chamber in which the biomass material moves in counterflow to the flue gases, the gas flow velocity being lower than the biomass velocity.

The preferred residence time of the biomass in the redox chamber is between 0.5 and 2.5 hours, depending on the type of biomass and its properties.

In one embodiment, after discharge from the redox chamber, the resulting waste product in the form of biochar is briquetted.

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The flue gases removed from the redox chamber are subjected to gas dust entraining before entering the combustion chamber.

The minimum residence time of the flue gas in the afterburner is 2 s.

In one embodiment, the electricity and heat production cycle is the Rankin Organic Cycle.

In another embodiment, the cycle for receiving electricity and heat is a steam cycle.

The advantages of the process according to the invention are expressed in the following: The thermal energy of the hot flue gases produced in the process of production of waste product in the form of biomass from biomass is utilized in a cycle for the production of electricity and heat. The method provides the production of biomass waste product by partial pyrolysis in a redox chamber in direct contact of the biomass with flue gases emitted by the burner and zonal maintenance of the oxidation and reduction atmosphere in the chamber without allowing combustion. of biomass material. Thus, the combined method of producing electricity, heat and waste product in the form of biomass from biomass provides higher overall efficiency when using small amounts of additional fuel.

Explanation of the attached figure

Figure 1 is a flow chart for the production of electricity, heat and biomass from biomass according to the invention.

Examples of carrying out the invention

The method according to the invention is illustrated by means of the flow chart presented in FIG. 1, and an exemplary embodiment of the invention which does not limit it.

The starting product is biomass and / or biomass waste - products of plant origin such as sawdust, bark, wood particles obtained from the fragmentation of wood waste from construction and demolition activities and the like. The biomass is fed through a chain conveyor 31 to a cleaning and flushing chamber 1 equipped with a coarse sieve, where large pieces (over 500 mm), stones and metal parts are removed. The biomass passed through the sieve by tape •

conveyor 32 is fed to a crushing plant 2, where it is crushed to a particle size of 50 mm, after which the crushed material passes through a sieve 2a. The water separated from the sieve 2a is returned to the cleaning and flushing chamber 1 by pump 2b, and the cleaned wood is fed via a second chain conveyor 33 and auger 34 to a drying drum 3 for partial removal of moisture from the crushed material. The gases from the drying drum 3 are passed through successively connected cyclones 3a and bag filters 3b and, using a suction fan 3d, the purified gases are discharged through the chimney Ze, and the partially dried biomass material is passed through a feed channel with a sealed chamber 4 and through auger feeders 5 and 6 connected via a non-return valve 7 is fed into the transition chamber 8a of a redox chamber, which in this example is a cylindrical rotary chamber 8 provided with a burner 9.

In rotary chamber 8, the shredded biomass moves counter to the flue gases generated by the burner 9 and is heated by direct contact of the biomass with the flue gases at a temperature between 150 ° C and 400 ° C under conditions of oxidizing medium (up to 10% excess of oxygen) in the upper zone of the rotary chamber and reduction - in the rest of the chamber. Under these conditions, partial pyrolysis takes place, without burning the biomass, and the moisture, volatile matter and gaseous products resulting from the partial pyrolysis contained therein are separated and passed into the flue gases.

The combination of the indicated temperatures and the composition of the gas phase in the rotation chamber 8 ensure the destruction of the hemicellulose contained in the biomass and converts it into gases (such as CO, aromatic hydrocarbons, ΟχΗχ and the like), organic liquids (such as acids, ketones, terpenes , phenols, paraffins, etc.), solids (such as coal, modified sugars, and polymeric substances), as well as mineral ash. The residence time of the biomass in the rotary chamber 8 plays an essential role in the biomass conversion process and is usually between 0.5 and 2.5 hours depending on the type of biomass and its properties.

The resulting waste product in the form of biochar with a temperature up to 400 ° C is unloaded from the rotary chamber 8 and is fed through a screw conveyor 36 into a product cooler 11 of a screw type, where it is cooled in an oxygen-free atmosphere, passed through a set of sieves 12, after which is conveyed to the mill 13 by means of a conveyor 37, the fine fraction of the milled material being fed through the second conveyor 38 to the briquetting machines 14, where it is mixed with adhesive additives and briquetted. The resulting waste product in the form of briquettes is removed for storage by means of belt conveyors 14c and 14d, and the dust released during the briquetting process passes through a cyclone battery 15 to remove the dust from the gas phase and with the help of the suction fan 16 the purified gas is takes away.

The flue gases emitted from the rotary chamber 8 above 150 ° C and calorific value up to 7400 kJ / w by pipeline 40 are passed through a cyclone type 17 particulate separator, and then fed to a combustion chamber 18 equipped with burners. The higher temperature and oxidizing medium in the afterburner 18 ensure complete combustion of C, CO and the volatile organic substances present in the flue gas, resulting in the flue gas temperature rising above 750 ° C. The 18 fumes removed from the combustion chamber typically contain 2 to 12% oxygen, 7-18% CO ₂ , up to 10% water vapor, between 5 and 30 ppmv NOx and the rest of the nitrogen. They are fed to a high temperature heat exchanger 10, which is used to pre-heat a flue gas recirculation (RDG) stream from about 20 ° C to about 670 ° C, and the 18 flue gases discharged from the afterburner are cooled to about 700 ° S.

After passing the flue gases through the high-temperature heat exchanger 10 through a pipe 41, they are fed to a second heat exchanger 21, where they heat a thermal agent connected to a Rankin Organic Cycle (OCR) circuit 22 to produce electricity and heat known to one of ordinary skill in the art. The OCR includes a turbine, a generator, a set of heat exchangers and an evaporator (not shown in the figure). The OCR circuit 22 is provided with a cooling water circuit 23, which in turn generates a considerable amount of heat that can be used for various purposes, for example, district heating, greenhouse heating and the like.

The electricity and heat production cycle may be of another conventional type, such as a steam cycle.

After the second heat exchanger 21, the flue gas stream at a temperature of about 110 ° C to 150 ° C, but not higher than the upper limit, passes through a conduit 42 to which bag filters 25 and a fan 30 are mounted, and then divided into two streams: one stream through tube 44 is fed to condenser 26, by which moisture is removed, and the other stream through tube 43 is fed to heater 24 and sent to the drying drum 3. The condenser 26 is fed with water by means of water pump 29. The dried gas stream representing said sweat k of RFA is • *

it is pre-heated in the high-temperature heat exchanger 10, located after the afterburner 18, after which it is sent to the rotary chamber 8 near the burner 9 via pipeline 46.

A forced draft suction fan 27 is mounted on the conduit 44 connecting the condenser 26 and the high temperature heat exchanger 10, which maintains a system pressure from the rotary chamber 8 to the outlet of the bag filters 25.

Claims (10)

Patent Claims 1. A method of producing electricity and heat from biomass by a continuous process, characterized in that it comprises the following steps: the crushed and partially dried biomass material is fed into a redox chamber equipped with a burner, where it is heated by direct contact of the biomass with the flue gases generated by the burner under conditions of oxidizing medium in the upper zone of the combustion chamber and in the rest of the chamber, at a temperature in the chamber between 150 and 400 ° C, partial pyrolysis of the biomass takes place, and the moisture, volatiles and gaseous products resulting from the partial pyrolysis are separated and passed through watts in the flue gas and the resulting charcoal solid is a waste product in the form of charcoal-like bio-coal with a calorific value close to that of brown coal; the waste product in the form of biochar is unloaded from the redox chamber; the flue gases containing the moisture, volatile matter and gaseous products of partial pyrolysis separated from the biomass are removed from the redox chamber and fed into a combustion chamber equipped with burners where complete combustion of the gases and the hydrocarbons contained therein is carried out to produce them. additional amount of heat; after removal from the combustion chamber, the flue gases are fed to a high temperature heat exchanger, where they heat a stream of recirculating flue gases fed back into the redox chamber; from the high-temperature heat exchanger, the flue gases pass through a second heat exchanger connected to a cycle for the generation of electrical and thermal energy, where the flue gas stream heats the agent used in the cycle; the flue gas stream leaving the second heat exchanger is split into two streams, one of which is said recirculating flue gas stream, which, after separation of the moisture contained therein, is fed to the high-temperature pre-heat exchanger, and then feeds back into the redox chamber; • the other flue gas stream is used to partially dry the biomass feedstock before being fed into the redox chamber. Method according to claim 1, characterized in that the oxidizing atmosphere in the upper part of the redox chamber, in which partial pyrolysis of the biomass is carried out, has an excess of oxygen of up to 10%. The method according to claims 1 and 2, characterized in that the redox chamber operates under pressure conditions in the range of 80 to 100 kPa (abs). A method according to claims 1, 2 and 3, characterized in that the redox chamber is a cylindrical rotary chamber in which the biomass material moves in counterflow to the flue gases, the gas flow velocity being lower than the biomass velocity . The method according to claims 1 to 4, characterized in that the residence time of the biomass in the redox chamber is between 0.5 and 2.5 hours, depending on the type of biomass and its properties. Method according to claims 1 to 5, characterized in that, after unloading from the redox chamber, the resulting waste product in the form of biochar is briquetted. Method according to claim 1, characterized in that the flue gases discharged from the redox chamber are subjected to gas entrapment before entering the combustion chamber. Method according to claim 1, characterized in that the minimum residence time of the flue gases in the combustion chamber is 2 s. A method according to claim 1, characterized in that the electricity and heat production cycle is the Rankin Organic Cycle. A method according to claim 1, characterized in that the cycle for generating electricity and heat is a steam cycle.