Development of preliminary design of the energy system of the Ningdong, Ningxia thermal power plant

. The purpose of this design is to master the basic steps, calculation methods, and equipment selection methods of the thermal power system of the thermal power plant, and to familiarize with the composition, connection, and operation characteristics of the thermal power system through the preliminary design of 600MW thermal power plant thermal power plant. This paper is divided into five parts, selecting the principle thermal system formulation, calculating the principle thermal system, the selection of unit auxiliary equipment, steam pipeline calculation, and selection after and after successful calibration. The preliminary design of the thermal system is completed by drawing the comprehensive thermal system diagram and the local system diagram using the above calculation data.


Introduction
At present, in China's power structure, thermal power generation accounts for 75.6%, hydroelectric power generation accounts for 23.5%, nuclear power generation accounts for 0.9%, and a small amount of the use of wind energy, solar energy, geothermal energy and ocean energy and other new energy to the area of renewable energy generation.For a long time, China's thermal power generation industry generated a unit capacity of 300MW units and low parameter units below the main, average coal consumption rate.Low efficiency, high emissions, and high coal consumption, the resulting environmental problems are becoming more and more serious, the national haze phenomenon has intensified, and people's lives are affected [1][2][3][4][5][6][7][8][9][10][11].
The 600MW unit is a supercritical unit with high efficiency, low coal consumption, a high degree of automation, fewer operators, etc.It also has the advantages of a short construction period, a small footprint of unit capacity, etc., which are suitable for China's national conditions.For this reason, Ningxia Nindong Power Plant N600MW is selected as the design topic to carry out the preliminary design of the thermal system of the 600MW unit.

Formulation of the principle thermal system
The principle thermal system is a detailed representation of the nature of the thermal process, the use of heat and energy conversion by the mass in the thermal system, and the influence of the thermal economy.The first step in the preliminary design of a thermal system is the appropriate formulation of the principle thermal system.

Development of feedwater reheat heating systems
In the drawing up of the feedwater reheat system, the choice for this design is three highpressure heaters, three low-pressure heaters, and one deaerator, with one shaft seal heater installed between the low-pressure heater and the condenser.

Preparation of the hydrophobic method for the heat recovery system
The hydrophobic method is divided into hydrophobic pumps and step-by-step self-flow, the design of hydrophobic selection of step-by-step self-flow method, the use of adjacent heaters on the steam side of the pressure difference so that the hydrophobic flow to the lower pressure heater.Select the step-by-step self-flow method, which has the advantages of spending less, the system is relatively simple, stable, and so on, the disadvantage is that the poor thermal economy, to reduce the disadvantages of the poor thermal economy of the step by step selfflow needs to be set up the steam cooler and hydrophobic cooler.The heater chosen is a surface heater, three high-pressure heaters are equipped with a steam cooler and hydrophobic cooler, and three low-pressure heaters are set up with a hydrophobic cooler.

Development of feedwater deoxygenation systems
The deaerator operation is divided into two ways: sliding pressure and fixed pressure, In this design the deaerator is selected to work under sliding pressure, and the deaerator sliding pressure operation has the advantage of improving the economy of operation.This is because the throttling loss of steam in the pump is avoided, and when the load is low, there is no need to switch the pump to higher pressure to pump out the steam, saving investment.At the same time, the turbine pumping points can be reasonably distributed, and with the slip-pressure operation, the high-pressure cylinder at all levels, including the high-pressure cylinder exhaust steam temperature will increase, which ensures the reheat steam temperature and helps to improve the efficiency of the heat cycle.

Supplementary water system development
Supplementary water can be supplemented to the deaerator and condenser in two places, In this design, the pressure of the deaerator is higher, and supplemental water to the condenser can improve the efficiency of the heat return system, so the choice of supplemental to the condenser as a better choice.
3 Calculation of the principle thermal system of a power plant This unit adopts 7-section non-adjustable steam extraction, corresponding to three highpressure heaters, one deaerator, and three low-pressure heaters, The deaerator adopts slidingpressure operation mode, and the parameters at rated working condition are shown in Table 3

Comprehensive thermal system development
The N600MW unit of Ningxia Ningdong Power Plant is equipped with a HG-2210/25.4-YM16supercritical primary intermediate reheat natural circulation boiler and a CLNJK600-24.2/566/566turbine with a rated output of 600MW.

Preparation of main and reheat steam systems
The main reheat steam system is divided into the single master control system, switching master control system, and unit system.For equipped with an intermediate reheat condensing steam unit according to the requirements of the choice of the unit system, the unit system not only has a relatively simple system, short piping, but valves can also save a lot of high-grade heat-resistant alloy steel and other characteristics, and accidents are limited to this unit, high safety and reliability.The reheat unit of the main steam, reheat steam system has a total of four types; dual-pipe system, single pipe -dual-pipe system, the main steam dual-pipe -single pipe -dual-pipe, reheat steam dual-pipe system, and the main steam and reheat steam are dual-pipe -single pipe -dual-pipe system.In this design, both are selected in the form of "double tube -single tube -double tube", which has the effect of cost savings to reduce the pressure drop and the cylinder temperature difference between the stress and friction of the shaft seal.

Formulation of the bypass system
The bypass system is divided into a three-stage bypass system, a two-stage bypass series system, a two-stage bypass parallel system, and a one-stage bypass system.In this design, the bypass system adopts a two-stage bypass series system, which can satisfy various requirements during startup through the coordination of a two-stage bypass system.The whole bypass system can also coordinate the startup parameters and flow, shorten the startup time, prolong the turbine's life, protect the work quality, reduce the noise, prevent the boiler from overpressure, and balance the steam balance between the boiler and the turbine.

Preparation of steam extraction and heat recovery system for steam turbine
According to the design requirements, the unit adopts a 7-stage heat return system, which consists of 3-stage high-pressure heaters, a 1-stage deaerator, and 3-stage low-pressure heaters.All the heaters are hydrophobic under normal working conditions by adopting selfflow mode step by step.High-pressure cylinder pumping and high-pressure cylinder exhaust steam for No. 1 and No. 2 high-pressure heater respectively; medium-pressure cylinder pumping and medium-pressure cylinder exhaust steam for No. 3 high-pressure heater and deaerator; low-pressure cylinder pumping for No. 5~7 low-pressure heater.There is also a shaft seal heater between the condenser and the No. 7 low-pressure heater.The deaerator adopts sliding pressure operation mode.

Preparation of water supply systems
The water supply system is divided into a single master control system, a switching master control system, unit system.As the design of the 600MW unit of the main steam piping is a unitary system, the choice of water supply system is also a unitary system, The advantages and disadvantages of the same with the main steam piping system, the system is relatively simple, short piping, fewer valves, the cost of spending less money to facilitate the centralized control of the machine and furnace and management and maintenance.

Preparation of the condensate system
The condensate system selected is the main condensate system, The main role of the condensate system is to send condensate from the condenser hot well to the deaerator, charging the vapor loss in the process of thermal cycle.
The 600MW unit operation feed pump is equipped with two sets of steam feed pumps with 50% capacity of maximum feed water and one set of speed-regulated electric feed pumps with 25%-30% capacity of maximum feed water as the startup and backup feed pump.This design uses a 50% capacity of the main steam feed pump and a 30% capacity of the electric feed pump; the main feed pump front pump is driven by the motor, the electric standby feed pump front pump and the electric pump is driven by the same motor; the electric feed pump is usually used in the start-up or low load conditions, the pump is also used as a standby pump.

Configuration and selection of feed pumps
According to the design specifications, the Ningxia Ningdong Power Plant N600MW unit is suitable for the configuration of two capacities of 50% of the maximum water supply steam feed pump and a capacity of 25% -30% of the maximum water supply speed control electric feed pumps for the start there is a standby feed pump.
The total DC feed pump outlet flow rate is 110% of the maximum continuous evaporation of the boiler.

Configuration and selection of condensate pumps
Ningxia Ningdong Power Plant shall have 2 condensate pumps.The capacity of each condensate pump shall be 100% of the maximum amount of condensate, and one of them shall be standby.

Configuration options for deaerator and feedwater tanks
Deaerator-rated output depends mainly on the unit's maximum feed water consumption, In the system heat balance calculation is generally taken as 105% of the maximum feed water, an intermediate reheat condensing unit should be used as a high-pressure deaerator.

Conclusion
This design mainly completed the following parts and calculations.
(1) Calculation and checking of the principle system of the power plant, calculation and checking of each power as well as economic indexes, the thermal efficiency of the whole plant, of which the standard coal consumption rate is , the thermal consumption rate of the whole plant is, the thermal efficiency of the whole plant is (2) Selection of unit equipment, calculation of outlet flow and head, power, and then consult the information on the relevant equipment for more appropriate selection.(3) Calculation and selection of the main steam pipeline, the pressure, temperature, inner diameter, and wall thickness of the calculation and selection of the appropriate materials, and then the flow rate calibration.(4) Comprehensive thermal system development.
In the process of the preliminary design of a thermal system of the N600MW unit of Ningxia Ningdong Power Plant, some problems with its design have been found, such as the choice of the hydrophobic method selected for this selection of the step-by-step self-flowing method, although the system is relatively simple, stable, etc., the disadvantage lies in the poor thermal economy, which is reflected in the later calculations, and we hope that the design of the future design will be selected for the hydrophobic pumps to achieve the improvement of the plant's economy.It is hoped that the hydrophobic pump will be selected in the future design of the hydrophobic design to achieve the purpose of improving the economy of the power plant.
Thanks to the other two authors for their contributions to this project.

, 1 ,
the coefficient of leakage loss of the whole plant work material b the steam of the shaft seal 02 0. = α sg , the inlet temperature of the E3S Web of Conferences 458, 01018 (2023) EMMFT-2023 https://doi.org/10.1051/e3sconf/202345801018supplemental water℃ = t ma20 , the specific enthalpy of the supplemental water is arrangement height is 26 m.Shaft seal parameters are shown in

Table 2 .
Shaft seal vapor volume and parameters