CN115773512A

CN115773512A - System for heating primary air of boiler

Info

Publication number: CN115773512A
Application number: CN202111047906.5A
Authority: CN
Inventors: 冯伟忠
Original assignee: Horgos Mingxuan Energy Technology Co ltd; Shanghai Shenneng Electric Power Technology Co ltd
Current assignee: Horgos Mingxuan Energy Technology Co ltd; Shanghai Shenneng Electric Power Technology Co ltd
Priority date: 2021-09-08
Filing date: 2021-09-08
Publication date: 2023-03-10

Abstract

The invention discloses a system for heating primary air of a boiler, which at least comprises the boiler, a primary fan, an air duct, a primary air heat exchanger, a coal mill and a primary air heat exchanger steam-water side system, wherein the primary air is not heated by a rotary air preheater and is heated only by the primary air heat exchanger. The invention thoroughly eliminates the primary air leakage caused by using the rotary air preheater, improves the adaptability of hot primary air to coal types, shortens the starting time and reduces the power consumption rate of a unit plant.

Description

System for heating primary air of boiler

Technical Field

The invention relates to a system for heating primary air of a boiler, and belongs to the field of thermal power generation.

Background

The traditional intermediate storage type pulverizing system has the problems of high pulverizing power consumption, large air leakage quantity, serious abrasion of an impeller of a powder exhauster and the like. Therefore, modern large coal-fired units generally adopt a positive pressure direct-fired pulverizing system, and accordingly primary air is required for drying and conveying pulverized coal and secondary air for combustion supporting. Meanwhile, in order to improve the combustion efficiency and the stable combustion property, the primary air and the secondary air need to be heated to a certain temperature before entering the hearth. Modern large boilers mainly use the heat of the flue gas at the tail of the boiler through a rotary air preheater to heat primary air and secondary air entering the boiler. The existing method for heating primary air by a rotary air preheater has the following problems.

Firstly, the rotary air preheater has a high air leakage rate, especially a primary air leakage rate. The air leakage phenomenon is one of the inherent attributes of the structure of the rotary air preheater, under specific dynamic and static gaps, the main driving factor of air leakage is differential pressure, and the pressure head of primary air is far higher than that of secondary air and flue gas. Therefore, the air leakage of the rotary air preheater mainly comes from air leakage caused by differential pressure between primary air and flue gas and between the primary air and secondary air, and the air leakage rate of the primary air usually reaches about 35% or even higher. The air leakage rate of the air preheater is too high, so that a plurality of problems can be caused: firstly, the air leakage directly increases the smoke discharge loss and the power consumption of the fan, reduces the boiler efficiency, increases the plant power consumption, and when the air leakage rate is too high, the powder feeding capacity and the drying output of primary air are reduced, and the boiler output is reduced. If air leakage of the air preheater is too large under high load, an induced draft fan is overloaded, so that the negative pressure of a hearth is difficult to maintain, and the load of a boiler is forced to be reduced for operation. Secondly, the average temperature of the smoke side is reduced by hot-end air leakage, so that the heat exchange capacity of the air preheater is reduced, the smoke exhaust temperature is lowered artificially by cold-end air leakage, the wall temperature of a heating surface of the cold end is lowered, cold-end corrosion and blockage are caused, the smoke side resistance is further increased, the heat exchange capacity of the air preheater is reduced, and a vicious circle is formed. Statistics show that for a 300MW unit, the air leakage rate of the air preheater increases by 0.66g/kWh for every 1% increase in the unit's integrated coal consumption.

Secondly, the adaptability of the hot primary air to coal types is poor. When the unit fires the coal type with lower moisture, in order to prevent that the wind powder temperature of coal pulverizer export is too high, have to take out partial cold primary air from the air heater entry, directly mix with the hot primary air of coal pulverizer entry to satisfy reasonable coal pulverizer entry primary air temperature demand, ensure the safe operation of powder process system. When the moisture of coal is high, the primary air temperature at the outlet of the air preheater is limited by the smoke temperature at the outlet of the economizer and cannot be adjusted upwards, so that the drying capacity and output of a coal pulverizing system are reduced, and the burnout rate of pulverized coal is influenced. Therefore, in the scheme of heating the primary air by the conventional rotary air preheater, the adaptability of the hot primary air to coal types is poor.

Thirdly, the time from the fuel oil to the pulverized coal in the starting stage is longer. The existing primary air heating principle is as follows: the high-temperature flue gas transfers heat to primary air through the heat storage element of the air preheater. In the starting stage, before fuel oil is put into use, the cold primary air cannot be heated because no high-temperature smoke is generated, after the oil gun is put into use, the temperature of the smoke flowing through the air preheater is low and the temperature rise rate is slow because the temperature of the heating surface in the furnace is low, so that the air-powder mixing temperature cannot reach the required putting temperature, and the putting time of the oil gun has to be prolonged. On one hand, the time from the fuel oil feeding to the coal powder feeding is prolonged, so that the starting energy consumption is increased; on the other hand, because the secondary air temperature of the boiler is low in the starting stage, the burnout rate of oil is low, and unburnt oil drops are attached to the SCR catalyst, the heat storage element of the air preheater and the electrode of the electrostatic dust collector, so that the performance of the equipment is influenced, and the risk of secondary combustion exists. Meanwhile, at the starting stage of the boiler, the electrostatic dust collector cannot be put into operation during the fuel oil feeding period, so that the serious pollution of the desulfurized gypsum slurry is easily caused, and the replacement amount and time of the gypsum slurry are increased.

Therefore, how to greatly reduce the air leakage rate of the rotary air preheater, improve the adaptability of the hot primary air to the coal types, and shorten the time from the fuel oil feeding to the pulverized coal feeding in the starting stage becomes an important issue.

Disclosure of Invention

In order to achieve the above object, the present invention provides a system for heating primary air of a boiler. The invention relates to a primary air system for heating a boiler, which at least comprises a boiler, a primary air fan, an air duct, a primary air heat exchanger, a coal mill and a primary air heat exchanger steam-water side system, wherein the air duct is connected with the primary air fan, the primary air heat exchanger and the coal mill, and primary air is heated only by the primary air heat exchanger without being heated by a rotary air preheater.

Further, the heat source of the primary air heat exchanger can be hot water or steam, and the primary air flows through the primary air fan, the primary air heat exchanger and the coal pulverizer in sequence.

Further, when the moisture of the coal for combustion is changed, the primary air temperature at the inlet of the coal mill is controlled by adjusting the flow and the temperature of the heat source of the primary air heat exchanger.

Further, the primary air heat exchanger comprises at least one primary air low-temperature heat exchanger and at least one primary air high-temperature heat exchanger which are sequentially arranged in series, and primary air sequentially flows through a primary air fan, the primary air low-temperature heat exchanger, the primary air high-temperature heat exchanger and a coal pulverizer.

Furthermore, the heat sources of the primary air low-temperature heat exchanger and the primary air high-temperature heat exchanger can be hot water or steam, and the temperature of the heat source of the high-temperature heat exchanger is higher than that of the heat source of the low-temperature heat exchanger.

Further, the air duct and the primary air fan of the boiler may be arranged in a single row.

The technical principle of the invention is that primary air is not heated by a rotary air preheater, and only primary air heat exchangers are used for heating primary air entering the boiler independently, thereby thoroughly reversing the design concept of the traditional boiler primary air system.

The invention has the following advantages: 1) The air leakage of primary air is completely avoided, and the air leakage rate of the rotary air preheater is greatly reduced. The primary air does not pass through the rotary air preheater, so that primary air leakage is completely avoided, the traditional three-bin air preheater can be changed into a two-bin air preheater, the size of the three-bin air preheater is obviously reduced, the differential pressure on the air smoke side is greatly reduced, and the air leakage rate of the rotary air preheater is correspondingly and greatly reduced. The design air leakage rate of the three-bin air preheater of a certain ultra-supercritical million units is 6%, and the design air leakage rate of the two-bin air preheater of a certain 1350MW unit is 3.5%.

2) The adaptability of the hot primary air to coal types is improved. According to the difference of the water content of the coal to be burned, the temperature of the hot primary air is adjusted by adjusting the heat source flow and the temperature of the primary air heat exchanger, so that the adjustability of the temperature of the hot primary air is enhanced, and the adaptability of the hot primary air to the coal is further improved.

3) The time from fuel oil feeding to pulverized coal feeding in the starting stage is shortened, and the starting energy consumption is reduced. The method for heating primary air by adopting the conventional three-bin air preheater is adopted, after an oil gun is put into use in the starting stage, the cold primary air is heated to the required temperature again after the temperature of flue gas flowing through the air preheater is gradually raised, and after the conditions are met, the pulverized coal can be put into use, usually, two hours or even more are needed from the time of putting the oil gun into use to the time of putting the pulverized coal into use. After the method is adopted, in the starting stage, before the oil gun is put into use, the primary air can be heated by adopting adjacent machine steam or feed water through the primary air heat exchanger, and the heated hot primary air enters the coal mill to heat the coal powder so as to meet the condition of putting the coal powder into use. Theoretically, when the operation is smooth, the pulverized coal can be put into use shortly after the oil gun is put into use, so that the starting time is greatly shortened, and further the starting energy consumption is reduced.

4) The boiler smoke exhaust loss is reduced, the plant power consumption rate of the unit is reduced, and the economical efficiency is improved. The primary air in the invention does not pass through the air preheater, and the air leakage of about 35 percent or even higher of the conventional primary air in the rotary air preheater is eliminated, so the flow rate and the pressure head of the primary air can be greatly reduced, the requirement of a unit can be met by adopting a single primary air fan, and the power consumption of the unit plant is further reduced. A certain 1350MW unit provided by the invention is provided with a single primary fan, the motor power of the unit is 4900kW (0.36% of plant power rate), while a certain conventional 1000 MW unit is provided with two primary fans, the motor power of the unit is 2X4200kW (0.84% of plant power rate), and the yield of reducing the plant power rate by 0.48% is brought.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a schematic diagram of one embodiment of the present invention.

The labels in the figure are: 1. a boiler; 2. A primary air fan; 3. an air duct; 4. a primary air heat exchanger; 41. a primary air low temperature heat exchanger; 42. a primary air high temperature heat exchanger; 5. provided is a coal mill.

Detailed Description

Example 1

Fig. 1 is a schematic view of an embodiment 1 of the system for heating primary air of a boiler according to the present invention. The system for heating the primary air of the boiler at least comprises a boiler 1, a primary fan 2, an air duct 3, a primary air heat exchange 4 (comprising a primary air low-temperature heat exchanger 41 and a primary air high-temperature heat exchanger 42) and a coal mill 5, wherein a heat source of the primary air high-temperature heat exchanger can be steam extraction of a steam turbine or high-temperature water supply, and a heat source of the primary air low-temperature heat exchanger can be steam extraction of the steam turbine or condensate water or return water of the primary air high-temperature heat exchanger.

The invention adopts the primary air low-temperature heat exchanger 41 and the primary air high-temperature heat exchanger 42 to heat all primary air step by step, and when the moisture of coal changes, the primary air temperature at the outlet of the primary air high-temperature heat exchanger is controlled by adjusting the flow and the temperature of the heat source of the primary air heat exchanger.

The primary air of the invention does not flow through the rotary air preheater for heating, but utilizes the primary air heat exchanger to independently heat all primary air entering the furnace, and has the following advantages:

1) The primary air leakage is thoroughly avoided, and the air leakage rate of the rotary air preheater is greatly reduced.

The primary air does not pass through the air preheater, so that the primary air leakage is thoroughly avoided, the traditional three-bin air preheater can be changed into a two-bin air preheater, the size of the air preheater is reduced, the differential pressure on the air smoke side is greatly reduced, and the air leakage rate of the air preheater is greatly reduced.

2) The adaptability of the hot primary air to coal types is improved.

According to the change of the moisture content of the coal to be burned, the temperature of the hot primary air is adjusted by adjusting the heat source flow and the temperature of the primary air heat exchanger, so that the adjustability of the temperature of the hot primary air is enhanced, and the adaptability of the hot primary air to the coal is further improved.

3) The time from fuel oil feeding to pulverized coal feeding in the starting stage is shortened, and the starting energy consumption is reduced.

The high-temperature heat source in the invention is steam extraction of a certain stage of the steam turbine (the steam extraction of the stage is simultaneously connected with adjacent machine steam) or high-temperature feed water (the high-temperature feed water is the feed water at the outlet of the heater corresponding to the adjacent machine steam or behind the outlet). In the starting stage, before the oil gun is put into use, primary air is heated through the primary air heat exchanger, heated primary air enters the coal mill to heat coal powder, the coal powder throwing condition is met as soon as possible, the coal powder can be put into use after the oil gun is put into use, the starting time is obviously shortened, and the starting energy consumption is further reduced.

4) The smoke exhaust loss is reduced, the plant power consumption rate of the machine is reduced, and the economical efficiency is improved.

According to the invention, a single primary air fan is adopted to meet the operation requirement of the unit, the plant power consumption rate of the unit is reduced, meanwhile, the air leakage rate of the rotary air preheater is obviously reduced, the boiler smoke discharge amount and the smoke discharge loss are correspondingly reduced, the power consumption of the induced draft fan is reduced, and the plant power consumption rate is further reduced.

It should be noted that one embodiment of the present invention has been described in detail above. According to the number and the connection mode of the heat exchangers, different heat sources of the heat exchangers and the like, the system connection mode with various arrangement combinations is adopted, and the invention aims to provide the system for heating the primary air of the boiler. Many modifications and variations will be apparent to those of ordinary skill in the art in light of the above teachings without undue experimentation. Therefore, the technical solutions that can be obtained by those skilled in the art through logic analysis, reasoning or limited experiments based on the existing methods based on the concepts of the present invention should be within the scope of protection determined by the claims.

Claims

1. The system for heating the primary air of the boiler at least comprises the boiler, a primary air fan, an air duct, a primary air heat exchanger, a coal mill and a primary air heat exchanger steam-water side system, wherein the air duct is connected with the primary air fan, the primary air heat exchanger and the coal mill.

2. A heating boiler primary air system as claimed in claim 1, wherein the heat source of the primary air heat exchanger can be hot water or steam, and the primary air flows through a primary air fan, a primary air heat exchanger and a coal mill in sequence.

3. A heating boiler primary air system as claimed in claim 2, wherein the primary air temperature at the inlet of the coal pulverizer is controlled by adjusting the flow and temperature of the heat source of the primary air heat exchanger when the moisture content of the coal burning coal changes.

4. A heating boiler primary air system according to claim 3, wherein the primary air heat exchanger comprises at least one primary air low-temperature heat exchanger and at least one primary air high-temperature heat exchanger which are sequentially arranged in series, and the primary air flows through a primary air fan, the primary air low-temperature heat exchanger, the primary air high-temperature heat exchanger and a coal pulverizer sequentially.

5. A heating boiler primary air system according to claim 4, wherein the heat source of the primary air low-temperature heat exchanger and the primary air high-temperature heat exchanger can be hot water or steam, and the temperature of the heat source of the high-temperature heat exchanger is higher than that of the heat source of the low-temperature heat exchanger.

6. A heating boiler primary air system according to claim 5, characterized in that the air ducts and the primary air fan of the boiler can be arranged in a single row.