CN213160221U

CN213160221U - Dilution air heating system suitable for urea hydrolysis ammonia production denitration system

Info

Publication number: CN213160221U
Application number: CN202021728713.7U
Authority: CN
Inventors: 刘闯; 贾冰峰; 王巍; 张广文; 徐梓原
Original assignee: North China Power Engineering Co Ltd of China Power Engineering Consulting Group
Current assignee: North China Power Engineering Co Ltd of China Power Engineering Consulting Group; North China Power Engineering Beijing Co Ltd
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2021-05-11
Anticipated expiration: 2030-08-18

Abstract

The utility model relates to a dilute wind heating system suitable for urea hydrolysis system ammonia deNOx systems, urea hydrolysis system ammonia deNOx systems contain the system ammonia district of hydrolysising, spout the ammonia grid, the system ammonia district of hydrolysising pass through the gas mixture pipeline with spout the connection of ammonia grid, dilute wind pipeline exit linkage in on the gas mixture pipeline, to letting in the dilution wind after the heating in the gas mixture pipeline, set up vapour-gas heat exchanger and 1 at least electric heater in order on diluting the wind pipeline, will dilute wind heating to 140 ℃ ~160 ℃ between, the utility model discloses a steam heat transfer and electric heating complex mode make and dilute wind all heatable to satisfying the temperature requirement under different operating modes, and the initial investment is low, and is little to unit operation economic nature influence.

Description

Dilution air heating system suitable for urea hydrolysis ammonia production denitration system

Technical Field

The utility model relates to a thermal power plant deNOx systems is applicable to the dilution wind heating that adopts urea system ammonia deNOx systems of hydrolysising.

Background

SCR method is mostly adopted for denitration in thermal power plants, and the reducing agent is mainly ammonia (NH)₃). According to the difference of raw materials and ammonia production process, the method can be divided into ammonia production by liquid ammonia, ammonia production by urea pyrolysis, ammonia production by urea hydrolysis and the like. Compared with liquid ammonia, the liquid ammonia takes urea as a raw material, has the characteristics of safety and reliability, does not relate to the problem of storage and transportation of dangerous goods, and is more and more widely applied in recent years. Compared with the pyrolysis method, the urea hydrolysis ammonia preparation method has the characteristics of low operation temperature, low energy consumption and the like, and is more and more widely applied in recent years.

The principle of the urea hydrolysis ammonia production is that a urea solution (the mass fraction of urea is about 40-55%) is heated to react urea with water to generate a mixed gas consisting of ammonia gas, carbon dioxide and evaporated water vapor. Generally speaking, the hydrolysis reaction temperature is 130-180 ℃, preferably 140-160 ℃, the temperature is too high, the energy consumption is large, the temperature is too low, the hydrolysis reaction cannot be activated, or the ammonia production rate is too low, so that the requirement of ammonia consumption is not met. The hydrolysis reaction is a reversible reaction, and the ammonia and the carbon dioxide are synthesized into the urea again at a temperature lower than the hydrolysis temperature. The temperature of the ammonia production, ammonia delivery and utilization systems and pipelines is strictly controlled.

After entering the SCR reaction zone, the mixed gas of ammonia gas, carbon dioxide and water vapor needs to be diluted first until the volume fraction of ammonia is not more than 5 percent, and then enters an ammonia injection grid. The dilution air can be flue gas, hot air or cold air. The ammonia spraying grid has requirements on medium cleanliness, so that smoke is not suitable for being adopted; the hot air at the outlet of the rotary air preheater carries a small amount of ash, so the adoption of the hot air is not the optimal choice. In the engineering, air (local air suction or cold air taken from the outlet of a primary fan and a secondary fan of a unit) is used as dilution air. Because ammonia and carbon dioxide can carry out reverse reaction to synthesize urea again under the condition of being lower than the hydrolysis temperature, the temperature of the mixed gas entering a reaction zone is ensured by keeping the temperature of a conveying pipeline, and the dilution air is required to be above the hydrolysis temperature, otherwise, the temperature after mixing is lower than the hydrolysis temperature, the urea is generated again by reverse reaction, and the ammonia gas which is the desired reducing agent cannot be obtained. Therefore, the dilution air at normal temperature needs to be heated to a temperature higher than the hydrolysis temperature, which requires a dilution air heating system.

The dilution air heating mode generally comprises a steam heating mode and an electric heating mode. The steam heating mode shown in fig. 1 is generally to heat the dilution air by using the unit extraction steam through the tubular steam-gas heat exchanger 6, which has the advantage of low energy consumption (compared with the electric heating mode, the energy can be saved by more than 50%). The electric heating mode shown in fig. 2 is to add an electric heater 7 on the dilution air pipe 5 to heat the dilution air, and has the advantages of simple system, low initial investment and high energy consumption. Steam heating is generally adopted in power plants.

The way in which the dilution air is heated by steam has a problem. First, the steam-gas heat exchanger 6 needs a large heat exchange end difference (generally, the end difference is about 15 to 20 ℃, and even if the heat exchange area is increased, the end difference is 10 ℃ or more) because the heat exchange coefficient of the gas side is low, for example, a heat source of 150 ℃ can only heat dilution air to about 135 ℃. The temperature of the steam heat source in turn depends on the steam pressure (the saturation temperature for the steam pressure minus the end difference is the temperature to which the dilution wind can be heated). Therefore, if the temperature of the dilution air is ensured to be above 140 ℃, a heat source of 155 ℃ is needed, and the corresponding pressure is not lower than 0.54MPa.

The thermal power generating unit hopes to adopt low-level steam extraction to heat dilution air (generally adopt the auxiliary steam, mostly four-stage steam extraction), and at this moment, the economy is good, and the operation regulation control is also convenient. But the four-stage extraction may not meet the extraction pressure requirement at low loads. Taking a certain 35 ten thousand supercritical unit as an example, under the working condition of 60% THA, the pressure of four-stage steam extraction is 0.555MPa.a, and the pipeline resistance is subtracted, so that the requirement of dilution air heating on a heat source is just met, namely the dilution air heating system can normally operate when the load of the unit is more than 60%. Below 60% THA loading, the extraction pressure will not meet the dilution air system requirements for the steam source. When the unit is loaded at 40%, the pressure of the four-stage steam extraction is 0.386Mpa, the corresponding saturation temperature is 142 ℃, and only the dilution air can be heated to 125-130 ℃, which causes the reverse reaction of ammonia and carbon dioxide.

The solution can adopt the extraction steam of higher stage position, leading from the cold section steam pipeline, but the pressure is too high (4.223 MPa.a under full load, 1.744MPa.a under 40% load), the temperature and pressure reduction is needed, and the pressure bearing capacity of the whole system can be improved by two grades, and the cost is increased. The cold section steam is used for heating dilution air, so that the economic efficiency of the unit is poor.

SUMMERY OF THE UTILITY MODEL

The utility model provides a technical problem lie in providing a dilute wind heating system suitable for urea hydrolysis system ammonia deNOx systems, adopts the mode of steam heat transfer and electrical heating combination, makes and dilutes the wind all can heat to satisfying the temperature requirement under different operating modes.

The technical means adopted by the utility model are as follows.

A dilution air heating system suitable for a urea hydrolysis ammonia production denitration system is characterized in that a dilution air pipeline for conveying dilution air to the urea hydrolysis ammonia production denitration system is sequentially provided with a steam-gas heat exchanger and at least 1 electric heater, and the dilution air is heated to 140-160 ℃.

Further, the urea hydrolysis ammonia production denitration system comprises a hydrolysis ammonia production area and an ammonia injection grid, wherein the hydrolysis ammonia production area is connected with the ammonia injection grid through a mixed gas pipeline; and an outlet of the dilution air pipeline is connected to the mixed gas pipeline, and heated dilution air is introduced into the mixed gas pipeline.

Furthermore, the steam-gas heat exchanger takes auxiliary steam as a steam source.

The utility model discloses produced beneficial effect: the utility model discloses only increase a small amount of initial investment (electric heater) and can solve the problem, electric heater's power can be very little, as long as can heat 140 ℃ from 125~130 ℃ with diluting the wind. Meanwhile, the operation economy of the unit is also slightly influenced, because the unit does not need to put the electric heater into operation at all under the load condition of 60 percent or more, the electric heater needs to be put into operation under the load condition of 60 percent or less, and the power is also very small, the influence on the operation economy of the unit is small, and the operation economy is better than that of a cold section steam heating mode and a pure electric heating mode.

Drawings

Fig. 1 is a schematic flow chart of a conventional system using a steam heating method.

Fig. 2 is a schematic flow chart of a conventional system using an electric heating method.

Fig. 3 is a schematic view of a system flow of the heating method of the present invention.

Description of the figure numbers:

1. a hydrolysis ammonia production zone; 2. a mixed gas pipeline; 3. an SCR reactor; 31. an ammonia injection grid; 32. a catalyst; 4. a dilution air supply device; 5. a dilution air duct; 6. a steam-gas heat exchanger; 7. an electric heater.

Detailed Description

Referring to fig. 3, the denitration system for ammonia production by urea hydrolysis includes a hydrolysis ammonia production area 1 and an ammonia injection grid 31. The hydrolysis ammonia-making area 1 is connected with an ammonia-spraying grid 31 through a mixed gas pipeline 2, and mixed gas of ammonia gas, carbon dioxide and water vapor generated in the hydrolysis ammonia-making area 1 is introduced into the ammonia-spraying grid 31.

The dilution air supply device 4 is connected to the mixed gas pipeline 2 through a dilution air pipeline 5, and introduces dilution air (air in this embodiment) into the mixed gas.

The utility model discloses a focus lies in, establishes ties in order on diluting wind pipeline 5 and sets up vapour-

gas heat exchanger

6 and 1 at least electric heater 7, will dilute the wind heating to 140~160 ℃ between.

The steam-gas heat exchanger 6 heats dilution air by using low-stage extraction steam, and in the embodiment, auxiliary steam (four-stage extraction steam) is used as a steam source. Similarly, taking a certain 35 ten thousand supercritical unit in the background art as an example, under the working condition that the THA is not less than 60%, only the steam-gas heat exchanger 6 is started, the electric heater 7 is not needed to be started, and the temperature of the heated dilution air can meet the requirement. When the load is lower than 60 percent THA, the auxiliary steam can not meet the requirement of the dilution air heating on the heat source, the electric heaters 7 are started group by group while the steam-gas heat exchanger 6 operates, the dilution air which can not meet the temperature requirement is heated for the second time, and the number of the started electric heaters is subject to the requirement of meeting the temperature. When the working condition is changed to four-stage extraction steam to meet the temperature requirement of dilution air, the electric heater 7 is closed.

That is, when the unit is operating at a low load condition (below 60% load) and does not meet the temperature requirement, the electric heating mode can be used as a supplement of the four-stage steam extraction heating mode at the low load.

Compare in the mode of simple adoption electric heater, the utility model discloses earlier utilize the auxiliary steam heat, whether nimble definite electric heater that needs carries out secondary heating for secondary heating's electric heater power can be very little, as long as can heat 140 ℃ from 125~130 ℃ with diluting the wind, the energy consumption is low.

Compare in the mode that only adopts the auxiliary steam to be the vapour source, the utility model discloses the auxiliary steam uses with the electrical heating cooperation, can realize that all can satisfy the heating requirement more than 60% load and below.

Compare in the heating method that adopts cold section steam to be the vapour source, the utility model discloses only adopt the electric heater that power is very little, equipment cost is lower, and need not set up temperature reduction pressure reducer and relief valve etc. can reduce about 20 ten thousand of first investments, and the bearing capacity of steam heat exchanger system is also low simultaneously, and electric heater only needs to drop into the operation under the low-load (below 60% load), and the electric heater power that needs the configuration is low (only need can dilute wind temperature rise 10~15 ℃ can), improves unit operation economy.

Claims

1. The utility model provides a dilute wind heating system suitable for urea hydrolysis system ammonia deNOx systems, its characterized in that sets up vapour-gas heat exchanger (6) and at least 1 electric heater (7) in order on diluting wind pipeline (5) that carry dilute wind to urea hydrolysis system ammonia deNOx systems, will dilute the wind and heat to 140~160 ℃ between.

2. The dilution air heating system suitable for the urea hydrolysis ammonia production denitration system of claim 1, wherein the urea hydrolysis ammonia production denitration system comprises a hydrolysis ammonia production zone (1) and an ammonia injection grid (31), and the hydrolysis ammonia production zone (1) is connected with the ammonia injection grid (31) through a mixed gas pipeline (2); the outlet of the dilution air pipeline (5) is connected to the mixed gas pipeline (2), and heated dilution air is introduced into the mixed gas pipeline (2).

3. The dilution air heating system suitable for the urea hydrolysis ammonia production denitration system of claim 1, wherein the steam-gas heat exchanger (6) takes auxiliary steam as a steam source.