Source: Dianlian Intelligent Manufacturing
Recommended unit: Huaneng Tongchuan Zhaojin Coal and Power Co., Ltd
Authors: Lv Yulin, Wang Gangfeng, Ma Zhanshun, Zhao Honglei
summary
Huaneng Tongchuan Zhaojin Coal and Power Co., Ltd. desulfurization wastewater zero discharge device is the first set of Huaneng Group Co., Ltd. using rotary atomization scheme of high-temperature flue gas bypass evaporation device, which is of great significance to achieve zero discharge of wastewater in the whole plant, and has a good demonstration and leading role for the system brother units, rotary atomizer is mainly used in the semi-dry desulfurization device of power plant, and the supersaturated lime slurry is atomized through the rotary atomizer, and the boiler outlet flue gas contact reaction is realized to achieve flue gas desulfurization. Huaneng Tongchuan Zhaojin Coal Power Co., Ltd., as the first power enterprise in Northwest China to realize the transformation of zero discharge of wastewater from the whole plant, applied the rotary atomizer to the flue gas evaporation device of desulfurization wastewater of 600MW unit for the first time, realizing the application innovation of the equipment, which has great demonstration significance and industry leading role in the field of environmental protection technology.
PART 1引言
China is a country with "more coal, less gas and less oil", and the proportion of coal in the mainland's petrochemical energy structure reaches 76%, and the clean utilization of coal resources is a major strategic deployment for national energy security. With the rapid and stable development of the mainland's economy and the increasing demand for social energy, the mainland's coal production and consumption have grown rapidly, and the total coal production and consumption have exceeded more than half of the world's, ranking first in the world. The rapid increase in coal consumption has not only provided energy power for the mainland's economic development, but also brought serious environmental problems.
More than 90% of China's industrial SO2 emissions come from coal combustion, and in recent decades, although the state has adopted environmental protection policies such as quota restrictions and pollution charges, the total annual SO2 emissions are still very large. In recent years, haze weather has gradually increased in the eastern part of the mainland, and the area polluted by acid rain has expanded rapidly, causing tremendous damage to crops, forests, and human health on the mainland, and has also become an important factor restricting the sustainable economic and social development of the mainland. With the improvement of people's living standards and the continuous strengthening of people's awareness of environmental protection, it is imperative to control SO2 emissions, and the concept of "lucid waters and lush mountains are invaluable assets" has been deeply rooted in the hearts of the people, and the rotary atomizer was first applied to the flue gas evaporation device of desulfurization wastewater of 600MW unit of thermal power plant, so that Huaneng Tongchuan Zhaojin Coal and Power Company has truly achieved zero discharge of wastewater from the whole plant, fully met the requirements of the pollutant discharge permit and environmental impact assessment, and effectively avoided the problems of wastewater discharge and excessive chloride ions in the desulfurization system.
PART 2 ZERO DISCHARGE SYSTEM FOR DESULFURIZATION WASTEWATER
The 2x600 MW unit boiler of the Phase I project of Huaneng Tongchuan Zhaojin Coal and Power Company is a HG-2070/17.5-YM9 boiler designed and manufactured by Harbin Boiler Factory Co., Ltd. using the technology introduced by ABB-CE combustion engineering company of the United States. The desulfurization wastewater zero discharge system adopts a single-side bypass flue gas evaporation process, the evaporation tower is configured with one furnace and one tower, using high-frequency rotary spray nozzles, and supporting ash conveying devices (only used as accident conditions), and the maximum design capacity of each unit is 8m/h. The high-temperature flue gas is connected to the evaporation tower from the flue of the denitrification outlet (air preheater inlet), and the desulfurization wastewater is evaporated in the evaporation tower. When the boiler is at full load and 75% load, the maximum wastewater treatment capacity can reach 8m3/h, the evaporator inlet temperature is 300 °C, the evaporator outlet temperature is not less than 150 °C, the air preheater outlet mixing temperature is 116 °C, and the bypass flue gas extraction flue gas volume is 3.3%-4.5% of the total flue gas volume.
2.1 The principle of treating desulfurization wastewater by the zero-discharge system of unilateral flue gas desulfurization wastewater.
The atomizer of the evaporation tower adopts the original imported atomizer of KS in the United States, including the atomizer body and the operating system, the processing capacity of a single atomizer is 8m3/h, the maximum speed can reach 16000r/min, and the normal operating speed is 15000r/ min, the flue gas is drawn out from the boiler unilateral denitrification outlet air preheater in front of a part, into the spray drying tower, the wastewater is pumped to the atomization disc in the atomizer, through high-speed rotation, the wastewater is thrown into 50-100μm fine droplets, the droplets are in contact with the high-temperature flue gas heat exchange, so that the water in the droplets volatilizes rapidly, the salts in the wastewater are dried and precipitated, mixed into the dust of the original flue gas, collected by the follow-up dust collector, the water vapor after the evaporation of the wastewater is mixed with the flue gas from the lower part of the spray drying tower, and dispersed into the ash for comprehensive utilization after the electrostatic precipitator collection。
2.2 Evaporation tower system equipment composition
Huaneng Tongchuan Zhaojin Coal and Power Company's desulfurization wastewater zero discharge system adopts a single-side bypass flue gas evaporation process, and the evaporation tower is configured with one furnace and one tower, using high-frequency rotary spray nozzles, and supporting ash conveying devices. The total height of the evaporation tower is 34.4m, and the steel structure is used as the main structure support. The total height of the tower is 27.2m, of which the cone section is 8.8m, which is used for the collection of deposited ash and the formation of a flow field conducive to the return of flue gas, and the straight section is 12.5m, which is used for wastewater evaporation.
Zero discharge system for desulfurization wastewater
The appearance of the whole set of equipment
Rotate the atomizer
PART 3: Collect data and model to optimize the flue gas flow field
Before the start of construction, the unilateral flue gas desulfurization wastewater zero discharge system treatment is carried out on the boiler system layout and flue direction, and the software simulation and optimization of the flue gas flow field of the evaporation tower are carried out, so as to provide technical support for the practical application of the project and lay the foundation for the good operation of the device.
3.1 Flue flow field simulation:
Arrangement of the original air preheater outlet flue
After the transformation, the flue air preheater outlet is arranged
Velocity gradient diagram of flue gas channel before reconstruction
Vector diagram of the velocity of the flue gas channel before retrofit
Diagram of the pressure gradient before the renovation of the flue gas flow channel
Velocity gradient diagram of flue gas channel after reconstruction
Vector diagram of the velocity of the flue gas channel after modification
Diagram of the pressure gradient after the modification of the flue gas flow channel
Diagram of the temperature gradient after the transformation of the flue gas flow channel
Simulation of flow field distribution in evaporation tower:
3D modeling of the flow area
Meshing of flow areas
Velocity contours
Temperature contours
Velocity vector illustration
Velocity size flow plot
3.2 Application of zero discharge system for desulfurization wastewater
Since December 15, 2019, Huaneng Shaanxi Tongchuan Zhaojin Coal and Power Co., Ltd. #1 and #2机组脱硫废水零放系统相继投入应用 have shown that the temperature distribution of the evaporation tower wall during the operation period has not deviated much from the temperature simulation, which meets the design requirements. In #1, #2机组等级检修期间对蒸发塔壁, and flue inspections, no tower wall ash and flue ash were found.
The temperature distribution of the tower wall under the maximum output operating condition of the zero discharge system of desulfurization wastewater
Operating parameters of each load section of the desulfurization wastewater zero discharge system
PART 4 Impact on boilers after the commissioning of the desulfurization wastewater zero discharge system
4.1 Effect on boiler efficiency
#1机组脱硫废水蒸发塔投运对锅炉效率的影响为0.24%, the impact on the coal consumption of the unit is 0.76 g/kW h, and #2机组脱硫废水蒸发塔投运对锅炉效率的影响为0 the impact on the coal consumption of the unit is 0.52 g/kW h, which meets the design requirements.
4.2 The impact of desulfurization wastewater on fly ash composition:
4.2.1 After spraying water, #1/#2机组灰库飞灰样品氯含量为0.105%/0.128% is mixed into cement according to the proportion of 40%, and the actual chlorine content of the final cement is 0.042%/0.051%, which is less than the above national standard for the chlorine content in fly ash Portland cement is not more than 0.06%;
4.2.2 After water spraying, #1/#2机组灰库飞灰样品游离氧化钙含量为0.92%/0.67% is mixed into cement according to the proportion of 40%, and the actual free calcium oxide content of the final cement is 0.368%/0.268%, which is less than the above national standard for the free calcium oxide content in fly ash Portland cement is not more than 1%.
4.3 The influence of the desulfurization wastewater system on the moisture content and flue gas temperature after it is put into operation
Under different load section test conditions, the flue gas moisture content and flue gas temperature were tested at the flue gas measurement points at the inlet and outlet of the evaporation tower.
Flue gas moisture content and flue gas temperature
According to the test results, the flue gas moisture content of the flue gas increases by 7.4%-11.2% after water spraying in the high and low load sections, and the flue gas extracted by the evaporation tower of the desulfurization wastewater zero discharge system is 4% of the total flue gas volume of the boiler, and the desulfurization waste discharge system of Huaneng Tongchuan Zhaojin Coal and Power Company has been put into operation for 2 years, and the influence of humidity on the subsequent flue gas cooler and electrostatic precipitator equipment has not been found, and the overall operating condition is good.
PART 5 Effect of unilateral flue gas desulfurization wastewater zero discharge system on boiler air smoke system
Huaneng Tongchuan Zhaojin Coal and Power Co., Ltd. #1, #2机组废水零排放系统蒸发塔均从锅炉单侧抽取烟气, after putting into operation, the exhaust gas temperature of the air preheater on the extraction flue gas side is reduced by 4-7 °C, and when the unit is connected with low load and the ambient temperature is below 0 °C, the average temperature of the cold end of the air preheater on the extraction flue gas side is 63-67 °C, which is lower than the acid dew point temperature, and the cold end of the air preheater has a safety risk of corrosion and blockage. Measures taken to solve this problem: 1) By adjusting the air supply volume of the blower on both sides and increasing the temperature of the heater, the temperature of the cold end of the air preheater is not lower than 70 °C to prevent the corrosion of the cold end of the air preheater; 2) By reducing the consumption of wastewater, adjusting the flue gas baffle to reduce the amount of smoke extraction gas of the evaporation tower, and controlling the temperature of the cold end of the air preheater above the acid dew point temperature.
PART 6 Innovative automatic control strategy for zero discharge system of desulfurization wastewater
The original automatic control strategy of the desulfurization wastewater discharge system is that the wastewater flow rate is used as the target value of automatic control, and the flue gas volume is used as the adjusted amount. According to the need to consume the maximum amount of wastewater during operation, the flue gas temperature at the outlet of the evaporation tower is set as the target value of automatic adjustment in the new design logic control, and then according to the hysteresis characteristics of the flue gas temperature change before and after the atomization of the evaporation tower, the automatic adjustment delay and adjustment dead zone are set in the logic according to the test results, and the automatic adjustment performance of the unit load is good when the load fluctuates between 180MW and 600MW after automatic operation.
PART 7 EXPERIENCE IN OPERATION ADJUSTMENT AND OVERHAUL AND MAINTENANCE
7.1 desulfurization wastewater evaporation tower in the normal operation of the basic ash, a large amount of ash mainly exists in the flue when the system is put into operation, ash into the tower, if not timely ash, there is a risk of ash blocking the flue, when the system is put into operation, keep the bin pump continuous ash conveying, to ensure that the ash entering by the flue can be transported away in time, when the system is in normal operation, PLC automatic control ash conveying automatically every 6 hours ash conveyance, to ensure that the ash inside the tower body is transported in time.
7.2 Rotating atomizer for a long time will cause fouling inside the atomization disc, resulting in the loss of dynamic balance of the atomization disc, the increase of vibration, and the damage of the atomizing disc will be caused if it is not dealt with in time.
PART 8引言
Single-sided flue gas desulfurization wastewater zero discharge system Huaneng Tongchuan Zhaojin Coal and Power Co., Ltd., as the first power enterprise in Northwest China to realize the transformation of zero discharge of wastewater from the whole plant, applied the rotary atomizer to the flue gas evaporation device of desulfurization wastewater of 600MW unit for the first time, realizing the application innovation of the equipment, and has great demonstration significance and industry leading role in the field of environmental protection technology.