Power unit system cooperating with the national power system

Abstract

Power unit system cooperating with the national electric power system (12), in which a steam generator (1) with a fuel inlet (7) and an air inlet (8) is connected at the output to a steam turbine (2) connected to a generator (3), which is connected through a billing system (11) to the national electric power system (12), and the steam turbine (2) is connected to a heat exchanger (4) to which a water pump (5) connecting back to the steam generator (1) is connected. After the generator (3), and before the billing system (11), there is drawn out a power line (10) which is divided into a power supply line for the feed water heater (13), which is connected to the electric feed water heater for the steam generator (15) located after the pump (5), and a power supply line for the air heater (14), connected to the electric heater of air or fuel-air mixture (16) for the combustion process in the steam generator (1), located before the air inlet (8).

Description

[0001] Power unit system cooperating with the national power system

[0002] Przedmiotem The subject of the invention is a power unit system cooperating with the national power system (NPS), implementing the concept of reconstruction of the technological line of energy redistribution in existing and newly designed power units. The purpose of the invention is to improve the operational flexibility of a steam power plant unit.

[0003] The term "flexibility of a steam power plant unit" is understood as the permissible range of load changes, defined as the ability to change the generated power from the maximum power to the technical minimum, while maintaining the ability to increase the generated power to the nominal value, as well as the permissible rate of load changes.

[0004] Concepts for improving the flexibility of steam unit operation proposed in the literature focus on thermal energy accumulation and utilization. They are described in the publications of Di Wang Deying Liu Chaonan Wang Yunlon Zhou Xiaoli Li MeiYang "Flexibility improvement method of coal-fired thermal power plant based on the multi-scale utilization of steam turbine energy storage " Energy Volume 239, Part D, January 15, 2022, 122301; Marcin Trojan, Dawid Taler. Piotr Dzierwa, Jan Taler, Karol Kaczmarski, Jan Wrona " The use of pressure hot water storage tanks to improve the energy flexibility of the steam power unit", Energy, Volume 173, April 15, 2019, Pages 926-936; Zhu Wang Ming Liu Junjie Yan "Flexibility and efficiency co-enhancement of thermal power plant by control strategy improvement considering time varying and detailed boiler heat storage characteristics" Energy Volume 232, October 1, 2021, 121048 or Badur, J., & Ziolkowski, P. (2019). Nowa koncepcja poprawy elastycznosci blokow parowych z zastosowaniem magazynow pary. INPE: Information on Electrical Standards and Regulations, 39-46.

[0005] In this study, it is proposed to use electricity to power an electric feedwater heater, which will increase the consumption of electricity to supply the steam unit's own needs, thereby reducing the value of power generated to the electric power system.

[0006] Regenerative boiler feedwater heating is one of the methods of improving the thermodynamic efficiency of the steam cycle. In the classical solution, the heat exchangers used to heat the water are supplied with steam from the steam turbine bleeds.

[0007] The use of an electric boiler feedwater heater in a steam power plant unit will allow the unit to increase the flexibility of its operation. In addition to reducing the value of the minimum power permanently generated into the system, also important, from the point of view of the flexibility of the steam power plant unit, is the speed of change in the value of power. In the case of increasing the own needs, by switching on the electric feedwater heater, we get the possibility of reducing the generated power very quickly, and in the case of withdrawal of this heater - the possibility of increasing very quickly the power generated to the power system.

[0008] Conversion of electricity to heat, including for water heating, is a technology that has been known for years. With the rapidly increasing installed capacity of renewable energy sources, the heating industry has been given the opportunity to use the imbalanced electricity produced in them (the so-called "Green Power to Heat", gP2H technology). The four basic technologies used in gP2H projects to convert electricity to heat are: electric resistance boilers, electric electrode boilers, resistance heaters, and heat pumps.

[0009] Resistive or electrode electric power-to-heat conversion technology can be used to electrically heat feedwater.

[0010] The wind and solar power plants connected to the NPS are characterized by a very high instability of the electric power generated and transmitted to the NPS. This instability causes serious repercussions in maintaining the certainty of electricity supply to consumers. This situation also leads to significant fluctuations in electricity prices in the balancing market, which in extreme cases can cause both their increase and significant decrease, even below the cost of generation, i.e. to the so-called "negative price". In order to maintain stability and certainty of electricity supply to consumers, it is expected that power plants and CHP plants operating in the NPS will ensure the widest possible range of high regulation of their generating units. It is therefore desirable to keep as many rotating masses of generators in the system as possible, while maintaining their high load recruitment and load shedding capacity. Depending on the length of the outage period, it takes a considerable amount of time and a high cost to re-synchronize the power unit with the NPS.

[0011] A well-known technical solution is the system of a power unit cooperating with the NPS, which is shown in the conceptual scheme in figure 1.

[0012] During start-up, before synchronization of the unit with the NPS, significant amounts of fuel are consumed, which generates dust and gas pollutants, including CO2, into the atmosphere. Delaying of the shutdown of a power unit, as well as shortening its start-up time under certain conditions, is technically, economically and environmentally justified. These conditions arise from the correlation of the price of electricity, the cost of restarting, the cost of fuel, the cost of purchasing a CO2certificate, revenues from services provided to the NPS, etc. The target customers of the new technology can be: international, national, regional and company power grids.

[0013] The inventive idea assumes the concept of modification of the technological line - energy redistribution system in existing and newly designed power units cooperating with the NPS. The proposed modification of the technological line includes a system for the distribution of electricity to supply the NPS and the unit's own needs. Electricity directed to the unit's own needs will be used to heat the boiler feed water or the fuel-air mixture. This will be done using electric heaters. Increasing the enthalpy of water and the fuel-air mixture can be carried out simultaneously or separately depending on the operating conditions of the unit. Power supply to the heat exchangers is carried out using electricity drawn before the settlement system from the NPS.

[0014] The subject of the invention is a power unit system cooperating with the national electric power system (NPS), in which a steam generator with a fuel inlet and an air inlet is connected at the output to a steam turbine. The steam turbine is connected to the generator, which connects to the NPS through a billing system. The steam turbine is also connected to a heat exchanger, to which is connected a water pump that connects back to the steam generator. Behind the generator and before the billing system with the NPS, a power line is brought out, which is divided into a line supplying electricity to the water heater and the air or fuel-air mixture heater.

[0015] Water and air (or fuel-air mixture) heaters are equipped with additional systems to support their operation. The electricity required to power them will be obtained from the same source as for powering the electric water and air heaters.

[0016] The water and air heaters are included in the unit circuit upstream of the steam generator and are equipped with independently operating electrical lines that draw power from the same source.

[0017] With the system that is the subject of the invention, the following functional -technical advantages are achieved:

[0018] • preservation of electrical power circulating in the national, regional, plant electrical grids, while preserving the electrical power injected into the NPS from the unit in operation and at a load below the minimum design technical capacity;

[0019] • increasing of the controllability of the power unit over its full load range;

[0020] • reducing of the number of start-ups and restarts of power units operated under different conditions of cooperation with the NPS;

[0021] • obtaining of special economic benefits in the situation of the occurrence of the so-called "negative prices" due to charges for overproduction of electricity supplied to the customer;

[0022] • the possibility of reducing the consumption of the basic fuel or using substitute fuel, which is cheaper and has different physico-chemical properties; • the possibility of building a system that realizes an increase in the energy of boiler water and / or air supplied for fuel combustion;

[0023] • rapid adaptation of existing structures to the expected operating parameters;

[0024] • the use of the electric water heating system minimizes the size of the necessary modernization works and their costs;

[0025] • the proposed system minimizes the inertia of the power redistribution system in the existing and newly built unit.

[0026] The growth of new generating capacity in Poland is too slow in relation to planned needs. Existing power plants are not kept sufficiently available and do not provide a guarantee of covering peak demand. The situation is not improved at this time by government relief planned for 2030, nor by the prospect of building new nuclear units after 2035.

[0027] The 200 MW class units are the basic, albeit oldest, coal-fired units in operation in Poland's power sector. It is becoming necessary to adapt the existing 200 MW units to the needs of the operation of the national power system (NPS). The biggest impediments to the unit's cooperation with the power grid include the flexibility of their operation, i.e. the ability to quickly switch on or off the unit. This is behind the high cost and lengthiness of the process. The proposed solution is to streamline this process, reduce its cost intensity and improve the conditions for cooperation of the unit with the power system saturated with RES sources. The same rationale applies to the operation of industrial units, ensuring continuity of production in plants.

[0028] The 200 MW class units are fired by coal or lignite and have been in operation for more than 50 years. We currently operate 47 units of this class in Poland (as of 2022): 16 - PGE, 15 - Enea, 10 - Tauron, 3 - ZEPAK, 3 - PKN Orlen with a total capacity of nearly 11 GW of electricity representing about 20% of the total generating capacity of the NPS. Among the first units to be modernized may be: Kozienice - 8 units of 200 MW, Polaniec - 6 units of 200 MW, and some of the oldest units of the Turow power plant. The modernization process should take place in stages due to the requirements of the NPS. The proposed modification includes a small-scale expansion of the technological system on the scale of the unit, which includes: taking electricity from the generator by increasing its own needs and then using it to stabilize the operation of the unit at small partial loads. The lower load thresholds for units in the range of 40-60% of nominal power, adopted in government regulations, are met by the proposed technology with surplus. This increases the utility of old units by making it more flexible in its ability to cooperate with the NPS, in which stochastic generation from RES sources (wind farms and photovoltaic).

[0029] Modifications to the units are aimed at reducing operating costs, lowering fuel consumption, reducing environmental burdens and better integration into the NPS. An additional effect of carrying out the modernization will be to extend the implementation period of new generation technologies, including nuclear, photovoltaic and wind in Poland.

[0030] The reasonableness of the proposed modifications resulting from the reduction of fuel consumption and improved cooperation of the unit with the NPS is proven by the following economic analysis. The analysis takes into account time-constant factors such as the unit energy consumption of the unit, the amount of atmospheric emissions, CIT, the cost of financing the WACC investment, and variable factors: projected inflation, allowing the determination of cumulative indices; the price of electricity, fuel and exchange rates. A 200 MW unit currently in operation in Poland was selected for the analysis, knowing its average annual power values, operating periods, number of starts and stops, etc.

[0031] The analysis of the economic impact associated with the modernization of the power unit was verified with a differential model. The reason for the choice of the differential model is the adoption of the prices of the main cost elements (price of coal, emission allowances) in relation to the assumed black power sales price, which show a negative Clean Dark Spread 1st degree margin, as well as negative results of the financial analysis. The proposed modification can be implemented at NPS production units (CUCDs - Centrally Dispatched Generating Units), the operation of which guarantees the operation of the electricity redistribution system. The proposed modernization of the CUCDs will guarantee a reduction in operating costs, thereby improving the producer's financial performance. The result achieved under the analyzed differential model is positive, which justifies the advisability of the proposed modifications. The differential model adopted in the analysis takes into account the necessary operating costs - without taking into account the other fixed and variable costs necessary for the operation of the generating unit. The analysis was carried out up to and including 2029, as all domestic power units of this type will be in operation by 2029. The analysis was carried out taking into account investments and the lack of additional bonuses for the investor for keeping the unit in the system at reduced capacity (the so-called spinning reserve). The analysis shows that by 2029 the NPV will exceed PLN 103 million, with an investment of PLN 2.8 million and a WACC of 15%.

[0032] The economic analysis carried out showed the reasonableness of the implementation of the proposed technology, as indicated by the positive value of the NPV index, with an assumed fixed cost of investment financing WACC.

[0033] In conclusion, the number of 200 MW units in operation, the continuous growth of installed capacity in renewable sources, characterized by stochasticity of electricity production, and the distant timing of the construction of new nuclear technologies, justify the advisability of modernizing existing units to improve their regulatory capacity in the NPS.

[0034] The invention is illustrated by means of a drawing. The state-of-the-art known layout of a power unit cooperating with the NPS in an ideological scheme is referentially shown in fig. 1. Fig. 2 shows an idea diagram the layout of a power unit cooperating with the NPS according to the invention.

[0035] An exemplary embodiment shows a power unit system cooperating with the NPS, consisting of a steam generator 1 with a fuel inlet 7 and an air inlet 8. The steam generator 1 is connected at its output to a steam turbine 2 connecting to a generator 3. The generator 3 by a power output line 9 connected, through a billing system 11, to the NPS 12. In addition, the steam turbine 2 is connected to the heat exchanger 4, to which the water pump 5 is connected, which connects back to the steam generator 1. Behind the generator 3 and before the billing system 11, the power output line 10 is divided into:

[0036] • the line supplying electricity to the feedwater heater 13,

[0037] • the line supplying electricity to the air heater 14.

[0038] The line supplying electricity to the feedwater heater 13 connects to the electric feedwater heater for the steam generator 15 located downstream of the pump 5, which is connected to the steam generator 1 by means of a pipeline 6. And the line supplying electricity to the air heater 14 connects to the electric heater of air or fuel-air mixture 16 for the combustion process in the steam generator 1 located upstream of the air inlet 8. The electricity required to supply them will be obtained from the same source as that for supplying the electric heaters for water and air.

[0039] Water heaters 15 and air (or fuel-air mixture) heaters 16 are included in the circuit of the unit upstream of the steam generator and equipped with independently operating electrical lines that draw power from the same source.

[0040] Reduction of the electrical power of the unit to its design minimum is carried out by reducing the amount of fuel burned in the steam generator 1. All the generated electrical power of the unit is then transferred to the NPS 12. If it is necessary to reduce the electrical power further, the power unit must be shut down. The inventive idea is realized in the technical possibility of transferring to the NPS 12 a smaller amount of electric power than the design minimum of the unit, while keeping the unit in operation. Which is performed as follows. Electricity is taken from before the billing system 11. The amount of electricity taken depends on the needs of the NPS and on the limitations on the side of the steam generator 1 resulting from the capacity. The electrical energy thus consumed increases the unit's own needs and is used to heat the working mediums in the built-in electric water heaters 15 supplying the steam generator 1 and the air 16 supplied for fuel combustion. As the load of the unit decreases, the temperature of the feed water decreases so the increase in the temperature of the feed water resulting from the operation of the electric water heater 15 causes the steam generator 1 to maintain a thermal output equal to or higher than the designed minimum production capacity. Heating of the incoming combustion air stabilizes this effect, and also results in increased protection of the rotary air heater from the effects of reduced exhaust gas temperature. The introduction of heat generated from the conversion of electricity in the water and air heaters into the combustion process results in a reduction in the amount of fuel burned in relation to the heat load of the steam generator. The described relationships are shown in fig. 3, which shows the thermal capacity of the boiler (Q), the electrical power of the generator (N) and the heat supplied in fuel to the boiler (B) as a function of the electrical energy output to the power grid (E).

[0041] In conclusion, the dynamic development of stochastic renewable energy sources (wind farms, photovoltaic) forces to improve the flexibility of steam units that maintain stable operation of the power system.

[0042] The priority of introducing electricity from the system from renewable energy sources forces frequent shutdowns of steam units to reserve and then their restarting which entails additional operating costs.

[0043] Application of the proposed invention will allow, from the point of view of the operator of a single power plant, to reduce these costs due to the possibility of keeping the unit in operation below its previous technical minimum.

[0044] It is expected that with the current and planned structure of the NPS generation sector in Poland's Energy Policy (PEP2040), all thermal units centrally disposed by the power system operator will be interested in implementation of the proposed solution. According to the information on generation resources provided on the NPS operator's website there are currently about 70 units of steam power plants.

Claims

ClaimPower unit system cooperating with the national electric power system, in which a steam generator with a fuel inlet and an air inlet is connected at the output to a steam turbine connected to a generator, which is connected through a billing system to the national electric power system, and the steam turbine is connected to a heat exchanger to which a water pump connecting back to the steam generator is connected, characterized in that after the generator (3), and before the billing system (11), there is drawn out a power line (10) which is divided into a power supply line for the feed water heater (13), which is connected to the electric feed water heater for the steam generator (15) located after the pump (5), and a power supply line for the air heater (14), connected to the electric heater 15 of air or fuelair mixture (16) for the combustion process in the steam generator (1), located before the air inlet (8)..

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