Notation for double-pressure waste heat boilers

§1 Introduction I. Brief Overview The gas discharged from a gas turbine after performing work still has a relatively high temperature, typically around 540°C. Utilizing the thermal energy of this gas can improve the thermal efficiency of the entire system. Usually, this heat is used to heat water, turning it into steam. Steam can be used to drive steam turbines and generators, as well as for heating in production processes or for domestic heating. In oil fields with heavy oil, steam can be directly injected into the oil wells to increase oil production. Depending on the various uses of steam, specific steam pressures and temperatures are required, which in turn necessitates steam generation equipment with different parameters. A device that uses the heat from gas turbine exhaust to generate steam is called a \"heat recovery steam generator,\" indicating that the heat from the exhaust is recovered; it is denoted by the acronym HRSG. In our country, it is commonly referred to as a “waste heat boiler”; this article also uses the term “waste heat boiler,” and the exhaust gas from gas turbines is simply called “flue gas.” “A “waste heat boiler” usually does not have a burner; if high-pressure and high-temperature steam is required, an additional burner can be installed inside the “waste heat boiler”. By burning fuel to raise the temperature of the entire flue gas, high-parameter steam can be generated. For example, in a waste heat boiler without a burner, the inlet flue gas temperature is 500°C; by installing an additional burner, this temperature can be raised to 756°C. The pressure of the steam can be increased from 4 MPa to 10 MPa, and its temperature can be raised from 450°C to 510°C. The steam can be used in high-temperature, high-pressure turbines, thereby increasing the electrical power output. Currently, the steam parameters of the waste heat boilers imported for use in China’s oil fields are: 4 MPa at 450°C, and 1.4 MPa at 195°C (saturated steam). The former supplies medium-pressure steam turbines for power generation, while the latter can be used for production or for heating in residential areas. Note: Regarding various types of waste heat boilers, these boilers utilize the exhaust gas from gas turbines to address the issue of afterburning. II. Composition of Waste Heat Boilers (I) Steam Generation Process Figure 19-1 shows a schematic diagram of the structure of a waste heat boiler, from which the steam generation process can be understood. Figure 19-1 Forced-circulation waste heat boiler (note that the evaporator is arranged in a co-current configuration, i.e., the tube bundle flows from bottom to top, to prevent vapor accumulation at the upper and lower elbows). ) The flue gas exiting the gas turbine flows through the flue to the inlet of the waste heat boiler; it moves from bottom to top, passing through the regenerator, two sets of evaporators, and the economizer, before being discharged into the chimney. The flue gas temperature is around 150–180°C; the flue gas temperature drops from 540°C to this level, and the heat released is used to turn water into steam. The feed water entering the waste heat boiler has a temperature of around 105°C. It first enters the upper economizer, where it absorbs heat and its temperature rises. Once the temperature reaches slightly below the saturation temperature corresponding to the pressure in the steam drum, the water leaves the economizer and enters the steam drum. The water that enters the drum mixes with the saturated water inside the drum, and then flows through the downcomer located below the drum to the circulation pump. There, the pressure of the water increases, and it then enters two sets of evaporators. Inside the evaporators, the water absorbs heat and begins to produce steam; usually only a portion of the water turns into steam, so what flows within the evaporator tubes is a mixture of steam and water. The soda mixture leaves the evaporator and enters the upper part of the drum. The drum is equipped with a steam-water separation device that separates steam from water; the water falls into the water space within the drum, while the steam exits from the top of the drum and goes to the superheater. Heat is absorbed in the superheater, converting saturated steam into superheated steam. Since the steam generation process has three stages, there should be three heating surfaces corresponding to them, namely the economizer, the evaporator, and the superheater. If superheated steam is not required and only saturated steam is needed, a superheater can be omitted. (II) Types of waste heat boilers 1. Forced-circulation waste heat boiler The waste heat boiler shown in Figure 19-1 is a forced-circulation waste heat boiler. The water that comes out from the bottom of the drum passes through a circulation pump before entering the evaporator; it is the power generated by the circulation pump that drives the circulation of the water, and this type of boiler is known as a \"forced-circulation waste heat boiler\". Its characteristics are ； The tubes of each heating surface component are horizontal, while the heating surfaces are arranged vertically, which saves floor space and reduces the height of the chimney at the outlet. However, a circulation pump is required during operation, which complicates things and increases maintenance costs. Currently, most of the waste heat boilers imported for oil fields use this type. 2. Natural circulation waste heat boiler Figure 19-2 shows a natural circulation waste heat boiler, in which the tubes of all the heating surface components are vertical. After absorbing heat in the economizer, the feed water enters the steam drum. The drum is connected to the lower header of the evaporation section via downcomers, which are located outside the flue and do not absorb heat from the flue gases. The drum is also connected to the upper header of the evaporator. The vertical tube cluster absorbs the heat from the flue gas. When water absorbs the heat from the flue gas, some of the water turns into steam. Since the density of steam is much lower than that of water, the average density of the mixture of steam and water in the vertical pipe is less than the density of water in the downward pipe. This difference in density drives the circulation of water. In other words, the water in the downward-flowing tube, which does not absorb heat, is heavier and flows downward. The steam-water mixture in the vertical pipe flows upward, resulting in a continuous steam generation process. At this point, the water that enters the evaporator flows not due to the power of a circulation pump, but as a result of the density difference of the fluid; such a waste heat boiler is called a \"natural circulation waste heat boiler\". Its feature is that it eliminates the circulation pump, simplifying operation and maintenance. However, the various heating surfaces are arranged horizontally, occupying a large area, and the chimney required at the smoke exhaust location must be tall. Figure 2 Natural circulation waste heat boiler. This article mainly introduces the “forced circulation waste heat boiler”. (Note: Generally, there are 5 circulation types for waste heat boilers: single pressure, double pressure without reheat, double pressure with reheat, triple pressure without reheat, and triple pressure with reheat.) ) (III) Layout of the waste heat boiler Figure 19-3 shows the layout of a forced-circulation waste heat boiler, including its heating surfaces and flue gas system. The features are as follows: Figure 19-3 Layout of the waste heat boiler 1. Flue gas system The high-temperature flue gas coming from the gas turbine has two exits: one leads to the waste heat boiler, from where the gas is discharged through the main chimney, while the other leads to a bypass chimney for gas discharge. Each flue is equipped with a baffle; there are three in total. The baffle on the main flue is called the \"main baffle\", the one on the bypass flue is called the \"bypass baffle\", and the baffle at the main chimney is called the \"chimney baffle\". All these baffles are used in conjunction with each other. Burning....

2# Fan Gong, I’ve learned something from this. Thank you

Q350 (364)/450 (275) – 48.5 (21) – 2.45 (0.3)/400 (200) 350 —— Flue gas flow rate at the inlet of Boiler No. 1, in Nm3/h 364 —— Flue gas flow rate at the inlet of Boiler No. 2, in Nm3/h 450 —— Flue gas temperature at the inlet of Boiler No. 1, in °C 275 —— Flue gas temperature at the inlet of Boiler No. 2, in °C 48.5 —— Superheated steam output of Boiler No. 1, in t/h 21 —— Superheated steam output of Boiler No. 2, in t/h 2.45 —— Superheated steam pressure of Boiler No. 1, in Mpa 0.3 —— Superheated steam pressure of Boiler No. 2, in Mpa 400 —— Superheated steam temperature of Boiler No. 1, in °C 200 —— Superheated steam temperature of Boiler No. 2℃

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Is Nm3/h the correct unit for Q350 (364) flow rate? Is there one more unit missing? ? For example: 10,000 Nm3/h

350,000 NM3/H – that’s the flow rate