ES2345760B1 - PROCEDURE FOR THE GENERATION OF ELECTRICITY FROM BIOMASS. - Google Patents

Abstract

Electricity generation procedure from biomass.

Procedure for the production of electricity from biomass, which includes the gasification steps of the biomass to produce a synthesis gas, burned gas from synthesis in a gas turbine to produce electricity and use of flue gases from the turbine outlet of gas as a heat source for additional energy production through a Rankine cycle, characterized in that during the cycle Rankine at least an intermediate steam overheating occurs of the working fluid of the Rankine cycle by heat input from the synthesis gas before said gas is combustion in the gas turbine.

Description

Electricity generation procedure from biomass.

The present invention refers to a procedure for generating electricity from biomass

More in particular, the present invention relates to improvements in the efficiency of integrated biomass gasification plants (Biomass Integrated Gasification Plants-BIGCC). While the invention is not necessarily limited to a certain type of biomass, the present invention is of special application to forest residues or lignocellulosic energy crops (for example Paulownia elongata ) In particular, for example, the use of urban waste and waste is envisaged. from cereals, although minor efficiencies could be obtained in this case.
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They exist in operation in different places integrated biomass gasification plants that operate with a similar scheme. In particular, several of them couple the gasification a combined cycle of electricity generation. Without However, the net efficiency of these plants must still be improved

More particularly, the combined cycle varies between BIGCCs.

Among the BIGCCs installed in Europe, you can cite, for example, facilities of Norrsundet (Sweden), Carbona (Denmark), Lausitz (Germany), Chianti (Italy), Lahti (Finland) and Güssig (Austria). The efficiency in production applications of Electricity of these plants varies between 20% and 35%.

Also, different facilities are known and production processes that combine a biomass gasification, a Brayton gas turbine cycle and a Rankine steam cycle.

Document US2007 / 0204620A1 discloses a utilization procedure of synthesis gas in which the gas of synthesis is directly burned, prior compression, along with water, in an aeroderivated gas turbine. Residual heat cycle Brayton is used in a Rankine cycle of a single turbine steam with a single stepped expansion in three stages. He thermal use of the procedure occurs in the generator of heat recovery steam that uses gases from exhausted combustion of the turbine. The water injected to the gas of synthesis causes corrosion problems and complicates the installation.

Document DE4342165C1, discloses a biomass gasification process with an energy use of the synthesis gas obtained by a combined cycle. The Gasification occurs at atmospheric pressure. Synthesis gas After passing physical and chemical cleaning phases, it must be cooled up to 30 ° C and subsequently compressed to be burned in the gas turbine. Synthesis gas is also used to be combusted directly for steam production in the cycle Rankine The Rankine cycle comprises a single steam expansion in A two phase turbine.

JP63140805 discloses a Electricity production procedure from biomass comprising a gasification, a combined cycle and a combustor Additional synthesis gas. The Rankine cycle is of type regenerative with an extraction that is taken to an exchanger Open type The mixture must then be pressurized and reheated, which limits the power of the turbine and complicates the installation. Rankine cycle fluid is vaporized and reheated using the heat input of the additional combustor of synthesis gas and of its flue gases. The mix of the open exchanger is vaporized and reheated using a mixture of gases from combustion from the gas turbine and combustor Additional synthesis gas.

Document US6032456B1 discloses a procedure for generating electricity that includes a pressurized gasification, hot desulfurization, Synthesis gas cooling and cold particle cleaning. The gas obtained is used in a combined cycle of a single gas turbine in which steam is evaporated by contribution of heat of the gasifier by means of an exchanger placed in the pressurized gasifier and flue gas exhausted

A main objective of the present invention is the improvement of the efficiency or energy efficiency offered by the known technique (defining efficiency or performance as the net power divided by consumption or net input).

To obtain this objective, as well as others additional objectives, the present invention focuses, among others points, in the improvement of gasification conditions and the thermal integration of the process. Also, the present invention it also provides preferentially the optimization of the cycle combined by incorporating three steam turbines with intermediate heating

Similarly, placement and conditions Operational Heat Exchangers of this invention and its preferred embodiments are such that the content Calorie extracted from the synthesis gas during cooling is used extensively.

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Also, in preferred embodiments, the The present invention also provides for a design of the conditions of burner operation such that combustion gases comply with environmental requirements of legal type.

More in particular, the present invention it comprises a procedure for the production of electricity at from biomass, which includes the gasification steps of the biomass to produce a synthesis gas, burned gas from synthesis in a gas turbine to produce electricity and use of flue gases from the turbine outlet of gas as a heat source for additional energy production through a Rankine cycle. In the procedure object of the present invention, during the Rankine cycle, at least one intermediate steam overheating of the cycle working fluid Rankine by heat input from the synthesis gas before said gas is combusted in the gas turbine.

In this way, the present invention causes a cooling of the synthesis gases by using which advantageously allows the synthesis gas to be cleaned (very preferably by chemical cleaning) after ceded heat to the working fluid of the Rankine cycle and before to be combusted in the gas turbine, having at that time the synthesis gas of an optimum temperature. The temperature of the Synthesis gases at the outlet of the gasifier is more than adequate to perform an overheating of the working fluid of Rankine cycle.

The Rankine cycle work fluid is preferably water.

In a novel way for this type of facilities, the present invention provides that the Rankine cycle understand three water vapor expansions with two intermediate reheating

More advantageously, in both overheating, the working fluid of the Rankine cycle is heated by heat from the synthesis gas before said gas is combustion in the gas turbine. This is advantageous thanks to the high temperature of the synthesis gas after gasification, it is convenient, however, to decrease its temperature, by what the utility obtained is double.

The gasification temperature is more suitable for the present invention when gasification occurs by partial combustion at a temperature higher than atmospheric. Yet more preferably the gasification of the present invention is Produces in a fluidized bed.

Preferably, the working fluid of the cycle of Rankine is evaporated using heat from the gases of combustion of the gas turbine, before entering a first phase of steam expansion of the Rankine cycle.

More preferably, after evaporation of the working fluid of the Rankine cycle, the steam obtained is reheated by heat input from the gas synthesis.

Also preferably, the synthesis gas undergoes a physical cleaning phase before exchanging heat with the working fluid of the Rankine cycle.

Even more preferably, said cleaning phase physics is carried out by passing the synthesis fluid through of some cyclones.

The control of the operating conditions of the procedure according to the present invention is of great importance for obtaining greater efficiency.

According to studies, tests and simulations performed by the inventor, the range of pressures Preference in which the gasification is carried out is between 5 and 15 Pub.

The preferred gasification temperature is between 800 and 1200 ° C.

Advantageously, the synthesis gas is combustion at a pressure of between 5 and 15 bar before entering the gas turbine in a burner that receives the synthesis gas and previously compressed air.

Also advantageously, the compressed air inlet on the burner to limit the gas turbine inlet temperature of the combustion of the synthesis gas at a maximum of 1300 ° C.

As for the expansion in the gas turbine, preferably, the gas gases will expand to a pressure of 1 bar and a temperature of approximately 650ºC.

As for the work ranges preferred by the present invention for the Rankine cycle, the fluid vapor of work will be reheated preferably up to a temperature between 350 and 500 ° C.

The maximum preferred fluid pressure of Rankine cycle work will be between 150 250 bar.

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The minimum working fluid pressure of the Rankine cycle (condenser pressure) will preferably be between 0.05 and 0.15 bar.

For a better understanding of the invention, attached by way of explanatory example but not limiting, some drawings of an embodiment of the present invention.

Figure 1 schematically represents a block diagram of a standard type BIGCC process example to which the present invention applies.

Figure 2 schematically represents a example of realization of a plant that carries out an example of process according to the present invention.

Figure 3 represents a diagram T-s (temperature-entropy) of a example of steam Rankine cycle applicable in one embodiment Especially preferred of the present invention.

Figures 1 to 3 illustrate an example of preferred embodiment of the present invention. The example shown it is a particular example of the present invention, which is not left necessarily limited by it.

The path indicated in figure 1 makes reference to the generation of electricity through a procedure IGCC (Integrated Gasification Combined Cycle) or BIGCC (Biomass Integrated Gasification Combined Cycle).

The example process starts with a pretreatment (1) of the biomass received and stored in silos (eleven). In the case of the example, the biomass can be waste forestry or lignocellulosic energy crops.

The biomass is extracted from a warehouse and transported to a mill (12) for particle size reduction from biomass to a suitable size to favor its subsequent drying and gasification. After the mill (12), the biomass is taken to a dryer (13) to ensure that the biomass moisture to the Gasifier input is less than 10% by mass. Drying can be performed by heat input to cause evaporation of the water and biomass moisture. Heat can, for example, come from synthesis gas, although any other source of heat it is possible, since the heat needed for drying is relatively small compared to the magnitude of the flows calories from the rest of the plant.

After pretreatment (1), the biomass passes to gasification process (2). To do this, it is sent to a gasifier (twenty-one). In the example shown, the gasifier (21) is a gasifier pressurized fluidized bed in which both biomass enters treated as a flow of pressurized air. The pressurized air is provided by a compressor (22) that takes air from the environment and that It is electrically operated.

Preferred operating conditions of the gasifier (21) are between 800 and 1200 ° C and between 5 and 15 Pub. The objective of incorporating a gasifier is to convert waste solid and liquid fuels in a gaseous or gaseous form (synthesis gas) that the gas turbine (63) can accept.

After the gasifier (21), the gas passes through a physical cleaning (3) by passing it through a series of cyclones (31), (32), (33) for the removal of ashes and other particles and impurities

Subsequently, the synthesis gases pass a cooling phase (4) in which they are refrigerated to a temperature that allows to carry out chemical reactions of Cleaning (5) of contaminants. The heat extracted from the synthesis gas it is used, at least partially, to generate superheated steam which will be expanded in turbines (72), (73), (74) of the cycle of Rankine In particular, in the example shown, the synthesis gas It is cooled in three heat exchangers (41), (42), (43). More particularly, in the first heat exchanger (41), the heat extracted to the gas is used to perform the first intermediate reheating of the Rankine cycle. In a second heat exchanger (42), the heat extracted to the synthesis gas is used to reheat steam from the evaporator (71) of the Rankine cycle (7). In the third exchanger (43), the heat extracted from the synthesis gas is used to get the second intermediate reheating of the Rankine cycle.

Also, although it has not been represented, the heat extracted from the gas could also be used for boilers of the cleaning unit (5). It can also be used to provide heat to the dryer (13) of the pretreatment phase (1) of the biomass.

After reaching a suitable temperature by assignment to the working fluid of the Rankine cycle in this case, water, the Synthesis gas enters the cleaning unit (51) in which Through chemical processes certain contaminants are removed. In particular, the elimination of nitrogen compounds is pursued and sulfur, which are precursors of acid rain and fog Photochemical toxic While the relatively low temperature of operation of the gasifier (21) and the deficit conditions of Oxygen thereof does not favor the formation of NO_ {x} and SO_ {x}, it is not possible to avoid the formation of the reduced forms NH3 and H2_S. Without the presence of the chemical cleaning phase (5), said reduced forms would later be oxidized, forming NO_ {x} and SO_ {x}, either in the combustor (61) or during the combustion gas circulation that occurs after combustion. The aforementioned reduced forms would contribute in this case. with 75-95% of the NO_ {x} emitted with the gases of combustion. Therefore, chemical cleaning contributes to the Elimination of 75-95% of emissions from NO_ {x}.

The formation of the remaining NO x compounds is of thermal origin, forming at high temperatures from N 2 the injected air. Different chemical cleaning methods (5) of These pollutants are well known to the expert in matter and, therefore, will not be explained in depth.

After passing the cleaning unit (51), the gas from clean synthesis feeds the combined cycle, which comprises a cycle Brayton (6) whose residual heat in turn feeds a Rankine cycle (7).

The example shown comprises a single turbine of gas (63) for the Brayton cycle (6) in which, after being burned in a combustor (61), the hot combustion gases are expanded to a temperature of approximately 650 ° C and 1 bar. These residual flue gases are used to generate the Rankine cycle steam (7), Preferably, the mass flow of compressed air introduced into the combustion chamber (61) by the compressor (62) of the Brayton cycle (6) is regulated to ensure a complete combustion and check that the temperature of the gases of combustion leaving the combustor (61) does not exceed 1300 ° C. By controlling this temperature the production of NO_ {x} of thermal origin and extends the life of the blades of the gas turbine (63).

As an advantage of the example procedure, it can be mentioned that the cycle of the example lacks compression of the synthesis gases Indeed, when gasification (2) is carried out in proper pressurization conditions, it is not necessary to compress the Synthesis gas prior to combustion, which avoids operating problems associated with the existence of a synthesis gas compressor. These problems are numerous due to the relatively high temperature of the synthesis gases, the existence of particles that have been able to escape from the cyclones and the possible existence of pressure pulses from the gasification process (2) and / or cleaned (3), (5). Also, at be pressurized, the conduits necessary to conduct the gases of synthesis through the cyclones (31), (32), (33), the heat exchangers (41), (42), (43) and the cleaning unit (51) are of a much smaller diameter and problems of load loss are avoided associated with the circulation of synthesis gas. Gasification pressurized contributes to increase global energy efficiency of the installation.

The Rankine cycle (7) operates with 3 turbines (72), (73), (74) with intermediate heating between each of the turbines Each turbine (72), (73), (74) works in conditions different. The Rankine cycle workflow in the example is Water.

The cycle (7) starts in the evaporator (71), in that the working fluid of the Rankine cycle, water in this case, is evaporated, reached the evaporation temperature corresponding to the maximum working pressure of the Rankine cycle. Heat input for evaporation is carried out by flue gases exhausted exiting the gas turbine (63). After leaving evaporator, the working fluid of the Rankine cycle is reheated in the second exchanger (42) going from there to the first turbine.

In the first turbine (72), the steam is expanded overheated from the maximum cycle pressure value to a first intermediate pressure value, after which the steam undergoes a first intermediate overheating in said first exchanger (41), receiving heat from the synthesis gas, reaching again, typically, the maximum temperature value reached in the first overheating mentioned above.

After the first reheating, the steam is expands in the second gas turbine (73) of the first value intermediate pressure at a second intermediate pressure value. After this second expansion, the steam is reheated a second time in said third exchanger (43), again until the third turbine and passes to the third gas turbine (7).

At the end of the last turbine the title of steam (x_ {v}) is preferably close to 1.

A capacitor (75) is incorporated to return at the beginning of the cycle saturated water. A suitable capacitor for this application can be, for example, a wind condenser (75).

After the condenser (75), a pump (76) carries the water to the maximum working pressure of the Rankine cycle and the it drives again to the evaporator (71), restarting the cycle. The operating conditions of the Rankine cycle (7) explained are shown in the T-s diagram for the working fluid (water) of figure 3. Figure 3 shows represented the cycle ideally, that is, without loss of Entropy in the expansion processes. It must be taken into account that there will be losses of entropy of the expansion processes that they would cause slight variations in the operating parameters real, but they are negligible for the purposes of the analysis that we occupies

In the present example, values are cited Especially preferred for the operating parameters of the plant. According to the simulations performed by the inventor, preferential steam operating conditions remain within the range 350-500ºC of maximum superheated steam temperature, 150-250 maximum operating pressure bar of water and 0.05-0.15 bar as water supply pressure to the cycle

Setting these conditions is essential for improve the net electric power produced during the process. The global energy efficiency obtained through the procedure object of the present invention, defined as the quotient between the net electrical power and the total heat output of the biomass used, reaches 40-42%.

Also, the process object of the present invention is able to meet administrative requirements in matters of emissions. It is estimated that the CO emission will be 10 times lower than currently imposed limits.

The maintenance of the gas turbine results Critical for the operation of the IGCC process. The life of the turbine may be shortened due to erosion and corrosion at high temperatures caused by the impact of particles e impurities present in gases, such as alkali metals. In Tables 1 and 2 summarize preferred maximum concentrations for the operation of a turbine suitable for the present invention. These requirements may vary depending on the manufacturer and model of gas turbine. The physical cleaning phases and chemistry must be designed taking into account these requirements

TABLE 1 Preferred specifications for the gas turbine. Trace elements with synthesis gas

one

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TABLE 2 Preferred specifications of other impurities for a gas turbine

2

All pressures given herein document are expressed as absolute pressures.

While the invention has been described with respect to examples of preferred embodiments, these are not due consider limiting the invention, which will be defined by the broader interpretation of the following claims.

Claims (21)

1. Procedure for the production of electricity from biomass, comprising the steps of gasification of biomass to produce a synthesis gas, burning of the synthesis gas in a gas turbine to produce electricity and utilization of the combustion gases of the output of the gas turbine as a source of heat for additional energy production by means of a Rankine cycle, characterized in that during the Rankine cycle there is at least an intermediate reheating of the steam of the working fluid of the Rankine cycle by means of heat input of the synthesis gas before said gas is combusted in the gas turbine. 2. Method according to claim 1, characterized in that the Rankine cycle comprises three expansions of the water vapor with two intermediate reheating. 3. Method according to claim 2, characterized in that in both superheats, the steam of the working fluid is heated with heat from the synthesis gas before said gas is combusted in the gas turbine. Method according to any one of claims 1 to 3, characterized in that the synthesis gas is cleaned after heat has been assigned to the working fluid of the Rankine cycle and before being combusted in the gas turbine. 5. Method according to claim 4, characterized in that said cleaning is a chemical type cleaning. Method according to any one of claims 1 to 5, characterized in that the working fluid of the Rankine cycle is evaporated using heat from the combustion gases of the gas turbine, before entering a first phase of steam expansion of the Rankine cycle. Method according to claim 6, characterized in that after evaporation of the working fluid of the Rankine cycle, the steam obtained is reheated by means of heat input from the synthesis gas. Method according to any one of claims 1 to 7, characterized in that the synthesis gas undergoes a physical cleaning phase before exchanging heat with the working fluid of the Rankine cycle. Method according to claim 8, characterized in that said physical cleaning phase is carried out by passing the synthesis fluid through cyclones. Method according to any one of claims 1 to 9, characterized in that the gasification is carried out by partial combustion at a temperature higher than atmospheric. 11. Method according to claim 10, characterized in that the gasification occurs in a fluidized bed. 12. Method according to claim 10 or 11, characterized in that the gasification is carried out at a pressure between 5 and 15 bar. 13. Method according to any of claims 10 to 12, characterized in that the gasification is carried out at a temperature between 800 and 1200 ° C. 14. Method according to any of claims 1 to 13, characterized in that the synthesis gas is combusted at a pressure between 5 and 15 bar before entering the gas turbine in a burner that receives the synthesis gas and air previously compressed. 15. Method according to any of claims 1 to 14, characterized in that the inlet of compressed air in the burner is regulated to limit the inlet temperature to the gas turbine of the flue gases of the synthesis gas to a maximum of 1300 ° C . 16. Method according to any one of claims 1 to 15, characterized in that in the gas turbine, the combustion gases expand to a pressure of 1 bar and a temperature of 650 ° C. 17. Method according to any one of claims 1 to 16, characterized in that in the Rankine cycle, the working fluid vapor is reheated to a temperature between 350 and 500 ° C. 18. Method according to any of claims 1 to 17, characterized in that the working fluid of the Rankine cycle is brought to a maximum pressure of between 150 and 250 bar. 19. Method according to any of claims 1 to 18, characterized in that the minimum working fluid pressure of the Rankine cycle is between 0.05 and 0.15 bar. 20. Method according to any of claims 1 to 19, characterized in that the working fluid of the Rankine cycle is water. 21. Method according to any of claims 1 to 20, characterized in that the biomass is forest residues and / or lignocellulosic energy crops.