JP4313257B2 - Black liquor power generation system and control method thereof - Google Patents

Description

  The present invention relates to black liquor-based power generation in a paper mill comprising a generator driven by a prime mover and a black liquor recovery boiler that generates steam by burning black liquor generated in the production process of producing paper from wood. The present invention relates to a system and a control method thereof.

  From the viewpoint of preventing global warming, in power generation facilities that use biomass such as thinned wood, which is renewable energy, as a fuel source, an increase in power generation efficiency and an increase in power generation are desired. In Europe and the United States, biomass power generation facilities that use wood resources as fuel as fuel are rapidly increasing due to government policies that support the effective use of renewable energy, and the capacity of power generation facilities exceeds 17,000 MW. However, biomass resources contain about 50% moisture, and even if dried, about 20% moisture remains. Therefore, power generation efficiency is as low as 14 to 18%, and improvement in efficiency is desired.

  On the other hand, in Japan, where 70% of the country is mountainous, the cost of collecting timber is high, so the biomass power generation of forest resources is 80MW in 1999, which is very small compared to Europe and America. For this reason, the utilization ratio of wood resources per 1 ha of forest is 1/3 to 1/4 of Sweden and Germany, and only about 1/3 of the annual growth of the forest is used. As a result, thinning work cannot be carried out properly, and the forest is overcrowded and vitality is lost. In addition, in the Kyoto Protocol ratified by Japan as a measure against global warming, “inclusion of carbon dioxide absorbed by sinks such as forests” is an important measure. In order to promote the use of thinned wood, which is a biomass fuel, and to maintain the vitality of the forest, it is necessary to develop a method of using it with high economic efficiency.

  In response to such social demands, in June 2002, the “Special Measures Act on the Use of New Energy by Electric Power Companies” (hereinafter referred to as the RPS Act) was enacted. As a result, credits are given according to the amount of power generated using renewable energy as a heat source in the power transferred through the power transmission system. General electric power companies and specific power generation companies are obliged to purchase these credits in proportion to the amount of power generated. By buying and selling credits through the market, the company aims to use renewable energy economically.

  Patent Document 1 is driven by a gas turbine generator, a black liquor recovery boiler that generates black liquor by burning black liquor generated in the production process of producing paper from wood, and the generated steam in a paper mill. A power generation system including a steam turbine generator is disclosed.

JP 6-82002 A (Overall)

  It is difficult to collect in the mountains, and domestic thinned wood is less economical than foreign chips. In order to use the thinned wood that can be produced in this country as a material for paper mills, it is necessary to improve the economy by utilizing the provisions for promoting biomass energy approved by the RPS Law. In order to be certified as electric power originating from renewable energy approved by the RPS method, it is necessary to transfer electric power generated by steam generated using black liquor as a fuel source and use it outside the paper mill.

  Even when the paper mill is connected to the power transmission system and can be used outside the factory, the paper mill operates continuously for 24 hours. Therefore, it is generally assumed that power is transmitted to the outside of the paper factory for 24 hours for sale. However, Japan's overall nighttime electricity demand is less than half the daytime peak. In order to increase the operating rate of electric power facilities, general electric power companies are trying to increase the consumption of night electricity by presenting a menu that greatly reduces the price of night electricity in order to promote the use of electricity at night. Therefore, there is a problem that the electric power price that can be used to sell electric power generated at night to a general electric power company or a specific electric power company is low and the economy is poor.

  When selling electricity outside the paper mill, the electricity sales price will be high if the amount of electricity generated is constant, but if the amount of generated electricity fluctuates greatly, it will be necessary to separately install equipment that adjusts the amount of electricity. Electricity prices will be lower. On the other hand, in a paper mill, the required steam and electric power fluctuate depending on the type of wood chips used as raw materials. The amount of power sold to the outside is an amount obtained by subtracting the amount of power consumed in the factory from the amount of power generated, and there is a problem that the amount of power that can be sold to the outside fluctuates.

  When the type of the wood chip that is the raw material changes, the calorific value of the black liquor supplied to the black liquor recovery boiler and the concentration of the inorganic chemical contained therein also change. Caustic soda and sodium sulfide, which are inorganic chemicals, are easily changed to SOx in a high temperature black liquor recovery boiler. If there is a low temperature area in the black liquor recovery boiler, a sulfuric acid liquid film is formed on the surface to form a heat transfer tube, etc. Corrodes. In order to operate a black liquor recovery boiler having a large heat capacity under constant conditions, it is desirable to make the thermal energy of the black liquor supplied to the recovery boiler as constant as possible.

  An object of the present invention is to provide an economical black liquor-based power generation system capable of effectively selling power generated by black liquor regeneration energy and a control method thereof.

  In a desirable embodiment of the present invention, a cogeneration facility including a generator driven by a prime mover, that is, a gas turbine, a diesel engine, or a gas engine, and an exhaust heat recovery boiler, or a combined system is installed in a paper mill. . With this cogeneration facility, power is generated using natural gas as a fuel source, and power is generated by a steam turbine using high-temperature and high-pressure steam using the exhaust heat. Steam at the required pressure is extracted from the middle stage of this steam turbine and used in the production process in the paper mill. On the other hand, the electric power generated by the steam generated in the black liquor recovery boiler using black liquor as a fuel source is sold to a general electric utility or a specific electric utility via a power transmission system such as an electric power company.

  In a preferred embodiment of the present invention, the cogeneration facility driven by the prime mover supplies electricity and steam for use in the paper mill, while increasing the output of the black liquor recovery boiler during the daytime, Decrease. Power is sold outside the paper mill only during the daytime.

  For this purpose, it is desirable to enlarge the storage tank for storing the concentrated black liquor before the black liquor recovery boiler, and to store the surplus portion with the concentrated black liquor generated by the evaporator at night. The amount of power that can be sold in the daytime is increased by burning the stored black liquor and the black liquor produced in the daytime with a black liquor recovery boiler that increases the output in the daytime to generate electricity. Here, the nighttime is a generic name when the power demand is low, and the daytime is a generic name when the power demand is high. Although the time period when the power demand is low varies depending on the region, it is generally a holiday from 10:00 on weekdays to 8:00 on the next day. Year-end and New Year holidays and Golden Week also correspond to times when electricity demand is low.

  Furthermore, it is desirable to provide a stirring function to keep the black liquor properties in the large tank provided in front of the black liquor recovery boiler constant, and it is possible to keep the composition of the black liquor supplied to the black liquor recovery boiler constant. It becomes.

  It is desirable to select a cogeneration facility in the paper mill that has a function to adjust the power and steam generation. When the demand for electric power and steam in the factory increases, the amount of electric power and steam generated in the cogeneration facility is increased, thereby making the amount of power sold outside the factory constant.

  The amount of power generated by black liquor that is separated from wood and recognized as renewable energy can be sold. For example, the credit for the RPS method can be obtained.

In general, a large-scale power plant has good power generation efficiency, but waste heat is discarded as it is to the environment. On the other hand, if a cogeneration facility is installed in a paper mill, the energy of fossil fuels can be used efficiently both in electricity and heat, and its spread is encouraged. In particular, a cogeneration facility using natural gas as a fuel source has a great effect in reducing CO ₂ generation because natural gas generates less CO ₂ per calorific value. Even if the power and steam energy demand in the factory fluctuates, the function of the cogeneration facility can cope with this, and a certain amount of power sold can be secured in the time zone when the external power demand is large. Since paper mills use a certain amount of electricity and steam for 24 hours in a row, the effect of reducing the amount of CO ₂ generated by introducing cogeneration facilities is also great.

  According to an embodiment of the present invention, 1) power can be sold at a time when power demand is high, and 2) fluctuations in the amount of power supplied to the outside can be reduced. Accordingly, it is possible to increase the power selling price and enhance the economic effect.

  In addition, since the amount of energy obtained by multiplying the black liquor properties supplied to the black liquor recovery boiler, the flow rate, and the heat generation amount can be kept constant, the durability of the black liquor recovery boiler can be greatly improved.

  Other objects and features of the present invention will become apparent from the following description of embodiments.

  Embodiments according to the present invention will be described below with reference to the drawings.

  1 and 2 are overall configuration diagrams of a black liquor-based power generation system of a paper mill according to an embodiment of the present invention. FIG. 1 is a configuration unit centering on a power generation system directly related to the present invention, and FIG. The component part centering on the papermaking process of a paper mill is shown.

First, the basic equipment configuration of the paper mill will be described with reference to FIG. FIG. 2 shows an outline of a pulp process and a papermaking process in a paper mill. A chip storage place in a paper mill carries a member obtained by cutting a board or square from a log, or a chip of about 3 cm square obtained by cutting a thinned material. In wood, about 50% of pulp, which is a constituent material of paper, is present, and the remainder is organic lignin and hemicellulose that bind pulp fibers. After the chips are heated, they are fed from the top to the digester 1 which is the first step of the pulp process. Here, lignin and hemicellulose are extracted from the chip using an inorganic chemical solution. For inorganic chemicals, a mixed solution of 70% caustic soda and 30% sodium sulfide is used, and under a pressurized condition of 170 ° C, the dissolution reaction proceeds continuously in the process of slowly flowing down in the cylindrical vessel of the vertical digester 1. . Lignin and hemicellulose dissolve in the inorganic chemical solution, leaving pulp fibers as solids. The continuous digester 1 has a pulp production capacity of 1,200-1,600 tons / day and a volume of 2,000 m ³ . In order to keep the digester 1 at a high temperature and a high pressure, 0.68 to 0.77 tons of heated steam is required to produce 1 ton of pulp depending on the type of tree.

  The slurry containing the pulp flowing out from the digester 1 is separated into a solid pulp and a solution by the multistage configuration of the pressure dephasor washer and the atmospheric pressure dephaser washer in the washing step 2. A solution called black liquor containing lignin and hemicellulose and having a concentration of about 15% is sent to the evaporator shown in FIG. On the other hand, the pulp is sent to the screen 3. On the screen 3, the pulp is “backed” to remove dust and freshly boiled chips contained in the pulp, and only good pulp is sent to the next bleaching facility 4.

  The bleaching equipment 4 is a four-stage process in which the pulp gradually increases in whiteness. In the digester 1, when 100% of the lignin is allowed to react with the pulp, the pulp fibers are also damaged. Therefore, the lignin is sent to the bleaching facility in a state where the lignin remains in the pulp, and oxygen is added at about 1.5 to 2.1% of the pulp weight at the first stage of the bleaching facility 4 so that the remaining lignin is 95 to 100 ° C. Remove under the following temperature conditions. In order to produce oxygen to be added, a PSA type oxygen production facility is provided in the paper mill. The bleached pulp is sent to the paper making process 5, where it is spread thinly and then dehydrated and dried to produce paper. Low pressure heated steam is used to dry the pulp containing a large amount of moisture.

  Next, a black liquor utilizing power generation system according to an embodiment of the present invention will be described in detail with reference to FIG.

  The black liquor separated in the cleaning step 2 in FIG. 2 is concentrated to a concentration capable of self-combustion by an evaporator 6 employing a multi-effect evaporator system, and then sent to a black liquor recovery boiler 7. In the multi-effect evaporator 6, heating steam is used in the first stage, but by reducing the evaporation pressure for each stage, the steam generated in the previous stage is used as a heating source in the subsequent concentration stages, thereby reducing heating. Concentration is possible by the amount of steam. In the final stage of the evaporator, a plate-type liquid film sulfidation evaporator is used, so that it is possible to concentrate to nearly 80%, which is close to the limit of fluidity. As a result, the black liquor keeps a high calorific value of 3000 Mcal / ton on average.

  Sodium sulfide contained in the black liquor generates corrosive SOx when burned. Therefore, in the black liquor recovery boiler 7, by using a corrosion-resistant material for the superheated tube or the like, steam of 500 ° C. or higher can be generated at 100 data even under conditions containing SOx. As a result, the power generation efficiency when the black liquor recovery turbine power generation facility 8 generates power using the steam generated in the black liquor recovery boiler 7 reaches 30 to 35%. This is a value nearly twice that of the case where power is generated by directly burning biomass in a boiler. By generating electricity with black liquor that has about half of the thermal energy possessed by the wood component, it is possible to obtain the same amount of power generation as wood power that burns everything, including pulp. The black liquor recovery turbine power generation facility 8 includes a steam turbine 81, a generator 82, and a condenser 83.

  Since the black liquor is burned and becomes high temperature in the black liquor recovery boiler 7, the inorganic chemical contained in the black liquor supplied to the digester 1 (FIG. 2) is the bottom of the black liquor recovery boiler 7 as a smelt that is a melt. Stays on. When impurities are removed from the green liquor in which smelt is dissolved in water, quick lime is added, and sludge is removed with a lime breaker and white liquor settler, the green liquor returns to the original mixed solution of caustic soda sulfide. This reusable white liquor is sent again to the digester 1 of FIG. 2 and used for dissolving the chips.

  The high-temperature and high-pressure steam generated in the black liquor recovery boiler 7 drives the steam turbine 81, generates electricity by the generator 82, and supplies it to the on-site power system 10 via the transformer 9. The on-premises power system 10 is connected to a power transmission system 11 of an electric power company.

  Steam is extracted from the middle stage of the steam turbine 81 and used as heating steam in the digester 1, the evaporator 6, and the paper making process 5. Although the steam pressure used in the digester 1 is high, the steam used in the evaporator 6 and the paper making process 5 may be low pressure. Since electricity is used in various processes in the paper mill, electric power is insufficient only by the amount of power generated by the steam from the black liquor recovery boiler 7. In order to make up for this shortage, conventionally, power is purchased through the power transmission system 11.

  As an equipment configuration according to an embodiment of the present invention, a large storage tank 12, a green liquor storage tank 13, a gas turbine cogeneration facility 14 are installed in an existing paper mill having a pulp production capacity of 500 ton / day with continuous operation for 24 hours. The facilities have been added. In addition, a flow rate control device 16 of a pump 15 that supplies black liquor from the large storage tank 12 to the black liquor recovery boiler 7 and a power sale command device 17 that instructs the flow rate control device 16 to sell power.

  The gas turbine cogeneration facility 14 includes a combustor 141, a gas turbine 142, a compressor 143, a generator 144, and an exhaust heat recovery boiler 145.

  A black liquor with a concentration of 15% is generated 210 tons per hour from the cleaning step 2 (FIG. 2) and supplied to the evaporator 6. Here, the black liquor concentrated to a concentration of 80% is stored in the large-sized storage tank 12 when the power demand is small. Since the calorific value of the black liquor generated from the evaporator 6 varies depending on the wood composition of the material, if the black liquor is supplied to the black liquor recovery boiler 7 as it is, the combustion state varies with time and the temperature distribution inside the black liquor recovery boiler 7 varies. Therefore, the valve 18 provided in the large storage tank 12 is opened, and the positive displacement pump 15 is driven so that the black liquor taken out from the lower part flows into the upper part, and the bulk storage tank 12 is provided with a partition for promoting the flow. Circulate the black liquor. In the system that leads from the large storage tank 12 to the black liquor recovery boiler 7, fluid resistance due to the burner in the black liquor recovery boiler 7 is generated in the black liquor. For this reason, it is desirable to measure the amount of black liquor supplied to the black liquor recovery boiler 7 by installing a flow meter 23 on the system from the pump 15 to the black liquor recovery boiler 7. Further, it is desirable to control the opening degree of the valve 18 based on the amount of black liquor obtained from the flow meter 23. As a result, the composition of the black liquor stored in the large storage tank 12 is kept uniform. The concentrated black liquor supplied from the evaporator 6 is supplied from the upper part to the large storage tank 12 so that it is not supplied directly to the pump 15. In addition, since the concentrated black liquor is combustible, the air inflow is suppressed as a sealed structure with a lid on the top, and a sprinkler is provided inside the large storage tank 12 in case of fire. Since the viscosity of the high concentration black liquor increases when it is cooled, a thin pipe is welded to the tank wall of the large storage tank 12 and the pipes before and after the pump 15 to keep the heat by flowing steam.

  In such a configuration, the black liquor recovery turbine power generation facility 8 and the gas turbine cogeneration facility 14 provide power and thermal energy necessary for the paper mill, and a certain amount of power is transmitted from the black liquor recovery turbine power generation facility 8. Sell power to 11. When the electric power and thermal energy required at the paper mill fluctuate, the fuel supply to the gas turbine cogeneration facility 14 is adjusted and dealt with to keep the electric power sold constant.

  As shown in the figure, the power sale command device 17 commands the power sale power to be constant during a predetermined time period (daytime), and commands zero during other time periods (nighttime).

  FIG. 3 is a graph showing a one-week power generation operation pattern in a paper mill according to an embodiment of the present invention. As is apparent from this graph, the gas turbine cogeneration facility 14 generates electric power and steam corresponding to 30% of the standard power demand of the factory and operates continuously for 24 hours. Although not shown in this figure, when the power demand of the factory fluctuates, the output power of the gas turbine cogeneration facility 14 is also controlled in accordance with the demand. On the other hand, the black liquor recovery turbine power generation facility 8 operates at a power generation output of 130% of the standard power demand of the factory from 8:00 am to 10 pm on weekdays and Saturdays, where power demand is high, and other power demands. When there is little time, it operates at 70% of the standard power demand.

  The black liquor recovery turbine power generation facility 8 has a function of reducing inorganic components contained in the black liquor and returning it to the original chemical, and it is difficult to operate at 70% or less of the standard output. In the operation pattern of FIG. 3, since the operation time of 130% output of the standard power demand is 84 hours per week and the operation time of 70% is 84 hours, it is the same as continuous operation at 100% output of the standard power demand. It is only possible to process black liquor.

  In FIG. 3, in the time zone when the power demand is low, the total output from the operation of the gas turbine cogeneration facility 14 and the black liquor recovery turbine power generation facility 8 just covers the demand for power and steam required in the paper mill. ing. When the power demand is high, the total operation output of the gas turbine cogeneration facility 14 and the black liquor recovery turbine power generation facility 8 is equivalent to 60% of the standard output, and is sold through the power transmission system. .

  By adopting the operation pattern of FIG. 3, it is possible to sell power only during a time period when the power demand is high and the power price is high.

  In a paper mill, the black liquor recovery boiler 7 has an important function of recovering caustic soda and sodium sulfide used for dissolving wood chips in the form of smelt. That is, sodium sulfide is produced by forming a reducing atmosphere inside and reducing sodium sulfate with the carbon content in the black liquor. Since the black liquor to be burned contains a large amount of sulfur components, some heat transfer tubes existing in the black liquor recovery boiler 7 are in a severe corrosive environment. However, since the black liquor recovery boiler 7 as a whole recovers the sulfur content in the form of sodium sulfide, the sulfur concentration at the outlet is low and there is no need to provide a desulfurization device in the subsequent stage. When the black liquor recovery boiler 7 is stopped, it is necessary to stop the operation of the entire factory. Therefore, the paper mill usually has a two-can black liquor recovery boiler.

  In the operation pattern of FIG. 3, the output is operated at 70% for 34 hours continuously from 10:00 on Saturday night to 8:00 on Monday morning. Since the concentrated black liquor produces 26 tons per hour, 7.8 tons corresponding to 30% is stored. Accordingly, the capacity of the large storage tank 12 needs to be at least 265 tons, and the scale is 300 tons with a margin.

  By making the black liquor property in the large storage tank 12 uniform, short-term fluctuations can be eliminated. Further, in order to keep the operating condition over a long period of time uniform, based on the temperature measurement result inside the black liquor recovery boiler 7, the positive displacement pump 15 The black liquor flow rate is controlled by changing the rotation speed. By providing the large storage tank 12, it is possible to control the amount of black liquor supplied to the black liquor recovery boiler 7 for a long time to an amount different from the amount generated from the evaporator 6.

  From the black liquor recovery boiler 7, 120 ton / 515 ° C. and 112 data high temperature / high pressure steam is generated and supplied to the steam turbine 81. During periods of high power demand, out of the amount of power generated by the black liquor recovery turbine power generation facility 8, power equivalent to 60% of the standard output not used in the paper mill passes through the on-site system 10 and the transmission system 11 to general electric utilities. Or, sell electricity to a specified electricity supplier or a wholesale power market that will be opened in the future. The steam depressurized by driving the steam turbine 81 is condensed by the condenser 83, boosted by a pump (not shown), and returned to the black liquor recovery boiler 7. The black liquor recovery boiler 7 can be operated only with black liquor in normal operation, but at the time of start-up, there is a possibility that unburned black liquor may remain in the apparatus at a low temperature inside the boiler. Therefore, in order to preheat the boiler at startup, it is necessary to add heavy oil to improve the combustibility. The amount of credit authorized by the RPS method is only the amount of energy of black liquor, which is biomass fuel, in the electric power carried by the power transmission system. Therefore, in order to evaluate the contribution ratio between the black liquor of the biomass fuel and the heavy oil of the fossil fuel among the electric power generated in the steam turbine 81, a meter for measuring the amount of heavy oil to be added is provided. At the same time, the flow rate of black liquor is also measured.

The gas turbine cogeneration facility 14 uses natural gas with a small amount of CO ₂ generation as a fuel. In the exhaust heat recovery boiler 145 utilizing the thermal energy held by the exhaust gas of the gas turbine 142 which is high temperature, two types of steam having different pressures of 1.5 MPa and 0.35 MPa are generated. The 1.5 MPa steam is mainly used as a heating source for a digester (not shown) that dissolves wood chips, and the 0.35 MPa steam is used for a heating source of the evaporator 6 and drying of pulp in the paper making process 5 (FIG. 2). . After the vapor used as the heat source is condensed and returned to the liquid, the impurities are removed and then pressurized and supplied to the black liquor recovery boiler 7. There is a difference between the balance between the amount of electric power and the amount of steam used in the factory and the balance between the amount of power and the amount of steam generated in the gas turbine cogeneration facility 14. Therefore, when the demand for steam is high, 0.35 MPa low-pressure steam is extracted from the steam turbine 81 and merged with the low-pressure steam generated in the exhaust heat recovery boiler 145 at the junction 19. Since the amount of steam generated in the exhaust heat recovery boiler 145 is mainly due to the latent heat of vaporization of water, the difference in the amount generated due to the difference in steam pressure is small. On the other hand, in the steam turbine 81, the power generation amount increases greatly as the extraction pressure is lower. Therefore, if the generation of high-pressure steam is borne by the exhaust heat recovery boiler 145 as much as possible and the supplement of the low-pressure steam is covered by the extraction of the steam turbine 81, the overall efficiency is improved.

  If other boilers already exist in the factory and the steam generated from the gas turbine cogeneration facility 14 becomes excessive, high-pressure steam is generated by the exhaust heat recovery boiler 145 and supplied to the steam turbine 81. It is also possible to increase the amount of power generation.

  The lignin and hemicellulose, which are organic substances contained in the black liquor in the black liquor recovery boiler 7, are combusted with air to form carbon dioxide and water vapor. After the steam is generated by the heat, they are released from the chimney. The non-combustible inorganic chemical component contained in the black liquor is deposited as a melt at the bottom of the black liquor recovery boiler 7 as a smelt. The smelt melt deposited in the lower part of the black liquor recovery boiler 7 flows down due to the pressure difference between the black liquor recovery boiler 7 and the atmosphere and its own weight. The smelt is finely dispersed with steam and dissolved in water in the tank to become a green liquor. This is temporarily stored in the green liquor storage tank 13. Since the recovery process 20 after the green liquor storage tank 13 has a capacity of only 100% of the standard output of the black liquor recovery boiler 7, when the black liquor recovery boiler 7 is operating at 130% output, a surplus of 30% Minutes are stored in the green liquor storage tank 13. Thereby, the difference of the installation capacity | capacitance of the collection | recovery process 20 and the generated green liquid flow volume is balanced. Since it is desirable that the capacity of the green liquor storage tank 13 is small, the smelt can be dissolved and stored in a high concentration state, and the concentration can be lowered by transferring moisture to the recovery step 20 when transferred.

  The recovery process 20 includes a green liquor settler 201, a causticizing tank 202, a white liquor settler 203, and a lime kiln 204. First, insoluble components such as unburned ash contained in the green liquor are settled and separated by the green liquor settler 201. In the next causticizing tank 202, quick lime is added to the green liquor from which impurities have been removed, so that sodium carbonate in the green liquor is changed to caustic soda and returned to the white liquor that is the original cooking chemical. The added quick lime becomes lime mud containing calcium carbonate as a main component in the causticizing tank 202. The white liquor settler 203 that separates the lime mud and white liquor can be separated from the lime mud by rotating a disk with a filter cloth in the pressurized white liquor settler and passing the filter cloth by the pressure difference. . The lime mud remaining on the filter cloth is scraped off by a blade and concentrated to a high concentration of 80%. This highly concentrated lime mud is sent to the lime kiln 204 and baked at a high temperature over several hours, returning from calcium carbonate to quick lime. Again, this quicklime is used in the causticizing tank 202 in the recovery process 20. Caustic soda and sodium sulfide, which are chemicals used in the paper mill, are regenerated to the original state in the recovery step 20.

  According to the above embodiment, the power sold to the power transmission system 11 outside the paper mill can be made constant power during a time when demand is high, and the economic efficiency by selling power and selling RPS credits is greatly improved. it can. Further, by providing the large storage tank 12 having a stirring function, it becomes possible to keep the black liquor supplied to the black liquor recovery boiler 7 constant, and the durability of the black liquor recovery boiler 7 can be greatly improved.

  FIG. 4 is a configuration diagram centering on a power generation system in a black liquor power generation system of a paper mill according to another embodiment of the present invention. In this embodiment, when the demand for electric power and steam in the factory fluctuates greatly, the amount of electric power sold to the outside is made constant by introducing a cogeneration facility that can actively control the output power and the steam output. Is.

  Regarding fluctuations in the required amount of steam, two countermeasures are provided: 1) providing a duct burner 146 inside the exhaust heat recovery boiler 145, and 2) providing a black liquor storage tank 21 in front of the evaporator 5. The duct burner 146 increases the amount of generated steam by burning natural gas in the middle of the boiler 145 and reheating the exhaust gas when the amount of steam is insufficient only by the exhaust heat of the gas turbine 142. As a result, the amount of steam can be adjusted by the amount of fuel input without affecting the operating state of other devices. The amount of water supplied to the subsequent stage of the boiler 145 may be increased in accordance with the fuel input amount of the duct burner 146. The cogeneration facility 14 capable of changing the amount of steam can be achieved not only by having the duct burner 146 but also by injecting steam before and after the combustor 141 or by combining a diesel engine and an exhaust heat boiler. Moreover, it is also possible to adjust electric power and steam generation amount by combining a plurality of devices such as a gas turbine and a small boiler instead of a single device.

  A black liquor storage tank 21 is provided as a countermeasure for changing the required steam amount in a short time. The evaporator 6 which is the main equipment that consumes the amount of steam in the paper mill reduces the flow rate of black liquor to be concentrated when the amount of steam is insufficient, and increases the flow rate of black liquor when the amount of steam is excessive. It can absorb the fluctuation of the required steam quantity in the factory. In order to keep the flow rate fluctuation and the generation amount of the evaporator 6 in equilibrium, it is possible to reduce the capacity of the large-sized storage tank 12 by providing the black liquor storage tank 21 in the previous stage of the evaporator 6.

  1) Diesel (or gas) engine power generation equipment 22 and 2) Back pressure turbine 147 are provided to cope with fluctuations in the amount of power required in the paper mill and increase the amount of power used in the factory. ing. Since the start-up time of the diesel or gas engine power generation facility 22 is generally shorter than that of the gas turbine cogeneration facility 14, it is easy to cope with fluctuations in power demand. Since the power generation efficiency of the cogeneration facility 14 that can use waste heat is higher than that of the engine power generation facility 22, the cogeneration facility 14 is mainly used for steady operation, and the diesel engine power generation facility 22 can be adapted to power fluctuations. desirable.

  A back pressure turbine 147 can also be provided to increase the amount of power generated. The steam pressure generated in the boiler 145 is increased to 15 MPa, the back pressure turbine 147 having an outlet pressure of 0.35 MPa is provided, and the energy when the steam pressure is reduced from 15 MPa to 0.35 MPa can be taken out as electric power. By extracting 1.5 MPa steam from the middle of the back pressure turbine 147, two kinds of steam of 0.35 MPa and 1.5 MPa can be provided as heating steam.

  Increasing the amount of power generation using black liquor, which allows RPS credits, as much as possible has a great effect on improving economic efficiency. Therefore, the following two functions are provided. In the configuration of FIG. 1, a part of the steam turbine 81 is extracted and used as heating steam in the factory. However, in the equipment configuration of FIG. 4, the steam amount is increased by the duct burner 146, and steam using black liquor as fuel is used. Do not use for heated steam. Next, before the circulating water from the condenser 83 is pressurized with a pump and supplied to the black liquor recovery boiler 7, it is heated by the feed water heater 84 to raise the feed water temperature at the inlet of the black liquor recovery boiler 7. When the feed water temperature rises, even if the black liquor recovery boiler 7 is heated with the same energy, the amount of generated steam increases and the power generation amount of the cogeneration facility 14 can also increase. Steam is extracted from the low pressure stage by the steam turbine 81 to this heating source. As a result, a so-called regeneration cycle is formed, and the amount of electric power that can be generated from the same black liquor fuel energy can be increased.

  According to this embodiment, it is possible to sell a certain amount of power to a general electric power company or a specific scale electric power company, it is possible to sell power at a high price, and the economic effect is increased.

The equipment block diagram centering on a power generation system among the black liquor utilization power generation systems of the paper mill by one Embodiment of this invention. The equipment block diagram centering on a papermaking process among the black liquor utilization electric power generation systems of the paper mill by one Embodiment of this invention. The graph which shows the electric power generation driving | operation pattern for one week in the paper mill by one Embodiment of this invention. The equipment block diagram centering on a power generation system among the black liquor utilization power generation systems of the paper mill by other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Digestion tank, 2 ... Cleaning process, 3 ... Screen, 4 ... Bleaching equipment, 5 ... Papermaking process, 6 ... Evaporator, 7 ... Black liquor recovery boiler, 8 ... Black liquor recovery turbine power generation equipment, 81 ... Steam turbine, 82 ... Generator, 83 ... Condenser, 84 ... Feed water heater, 9 ... Transformer, 10 ... On-site power system, 11 ... Electric power transmission system, 12 ... Large storage tank, 13 ... Green liquor storage tank, 14 ... Gas turbine cogeneration equipment, 141 ... combustor, 142 ... gas turbine, 143 ... compressor, 144 ... generator, 145 ... exhaust heat recovery boiler, 146 ... duct burner, 147 ... back pressure turbine, 15 ... pump, 16 ... flow rate Control device, 17 ... Electric power selling command device, 18 ... Valve, 19 ... Junction point, 20 ... Recovery process, 21 ... Black liquor storage tank, 22 ... Diesel (or gas) engine power generation equipment, 23 ... Flow meter

Claims (5)

  In a power generation system comprising a black liquor recovery boiler that generates black steam by burning black liquor produced in the process of producing paper from wood, and a steam turbine generator driven by the generated steam, in a predetermined time zone And a power selling power control means for increasing the amount of black liquor supplied to the black liquor recovery boiler and increasing the amount of power transmitted from the steam turbine generator to the power transmission system during the predetermined time period. Black liquor power generation system.   2. The black liquor power generation system according to claim 1, wherein the power selling power control means is configured to control the power selling power to be substantially constant over the predetermined time period.   In Claim 1, it is provided so that black liquor may be supplied to the said black liquor collection | recovery boiler, The amount of black liquor required for black liquor electric power generation more than the electric energy which the capacity | capacitance is going to transmit to the said power transmission system on the 1st is stored A black liquor power generation system characterized by a black liquor tank.   A generator driven by a prime mover, a black liquor recovery boiler that generates black liquor by burning black liquor produced during the production process of paper from wood, and a steam turbine generator driven by this generated steam In the power generation system, the power selling power control means for increasing the amount of black liquor supplied to the black liquor recovery boiler in a predetermined time zone and increasing the amount of power transmitted from the steam turbine generator to the power transmission system, and the production A black liquor-based power generation system comprising power generation control means for controlling power generated by the generator in accordance with power consumption in the process. A method for controlling a power generation system comprising a black liquor recovery boiler that generates steam by burning black liquor produced in the production process of producing paper from wood, and a steam turbine generator driven by the generated steam. A black liquor-based power generation system control method characterized in that the black liquor supply amount to the black liquor recovery boiler is increased during a predetermined time period to increase the amount of electric power transmitted from the steam turbine generator to a power transmission system.

Images