What should be paid attention to when debugging wet desulfurization?

As the country has paid more attention to environmental protection in recent years, in order to meet environmental protection requirements, the desulphurization of high-sulfur flue gas in my country's cement industry has become a general trend. At present, limestone-gypsum wet desulfurization technology is mainly used for high-sulfur flue gas desulfurization of cement kilns in China. This article mainly summarizes the precautions in the commissioning of cement wet desulfurization.

In order to make the installed cement kiln tail flue gas wet desulfurization system smoothly put into production and operation and ensure that the environmental protection indicators meet the design requirements, the system needs to be debugged before it is put into production. In order to ensure the smooth progress of the debugging work, this article will summarize the precautions in the single, sub-system, linkage debugging and system operation.

1 Unit debugging

The monomer commissioning of the cement wet desulfurization system includes the trial operation of the motor, the transmission test of the chain protection, the transmission test of the valve, the water injection of the tanks in the system, and the switch transmission of the rotating equipment. During the trial operation of the motor, attention should be paid to the forward and reverse rotation of the motor, especially to avoid idling and reverse rotation during the trial operation of the circulating pump, so as to ensure the safety of personnel and equipment during the trial operation. The interlocking test is to ensure that the interlocking can be realized when the system is running, and the interlocking can be triggered when the interlocking conditions are met, so as to ensure the safety of the equipment and the normal operation of the system.

2 points system debugging

The wet desulfurization system mainly includes process water system, flue gas system, absorption tower system, absorbent preparation and supply system, wastewater system, gypsum dehydration system and accident slurry system.

2.1 Process water system

When the process water system is debugged, the water pump should be adjusted to adjust the outlet pressure of each pump. The outlet pressure should meet the needs of the system. The pressure should not be too high or too low, especially the flushing water pressure of the demister. Low pressure is not conducive to the demister. Flushing, too high pressure will damage the demister flushing pipeline, so the outlet pressure of the water pump should be adjusted to the design range. Attention should be paid to flushing the pipeline during commissioning, and special attention should be paid to the flushing water of each instrument. When debugging the defogger flushing water, pay attention to checking the flushing effect, as shown in Figure 1, and test the flushing sequence to ensure that the time meets the design requirements.

Figure 1 Flushing effect of demister

2.2 Absorption tower system

The absorption tower system is the core of the entire desulfurization system, and the chemical reactions of the desulfurization system are carried out in the absorption tower. Therefore, the quality of the absorption tower should be strictly controlled during the design, construction and later commissioning so that it can meet the needs of desulfurization. In the commissioning of the absorption tower system, special attention should be paid to the commissioning of the circulating pump. The motor forward and reverse commissioning and the motor trial operation should be completed before starting to ensure the safe operation of the circulating pump. Remember that the circulating pump must not run idle and reverse. During trial operation of the circulating pump, attention should be paid to check the atomization effect of the spray layer to ensure that the coverage area of the spray layer can meet the design requirements. as shown in picture 2.

During the desulfurization reaction process, the formation of gypsum requires the blowing of oxidizing air to forcibly oxidize the intermediate product. Because the temperature of the oxidizing air blown by the oxidizing fan is relatively high, if the oxidizing air is not cooled, the oxidizing air in the tower in contact with the slurry will be at a high temperature for a long time, and it will scale on the oxidizing air pipeline, which will block the oxidizing air pipeline for a long time. Affect the oxidation efficiency, thereby reducing the desulfurization efficiency. Therefore, attention should be paid to the input of cooling water when the oxidation fan is running.

Figure 2 Atomization effect of spray layer

2.3 Absorbent preparation and supply system

The absorbent preparation and supply system should focus on checking the delivery pipeline to ensure that the slurry can be smoothly delivered to the absorption tower. It should be noted that sufficient absorbent slurry has been prepared before the desulfurization system is put into operation. The absorbent is generally selected from the ash return of the kiln tail waste heat boiler, the humidification tower, and the kiln tail dust collector. Because the cement kiln does not produce ash during the ignition process for a long time, generally up to 18 hours, and the ignition process will produce sulfur dioxide that needs to be removed, so it is necessary to prepare enough absorbent slurry.

2.4 Wastewater system

The waste water of the desulfurization system comes from the filtrate water produced by the gypsum dehydration system, part of which is returned to the absorption tower for reuse, and the other part is transferred through the filtrate clarification tank and transported by the waste water pump to the cement kiln head grate cooler for evaporation treatment, which can achieve zero waste water discharge. Pay attention to the working conditions of the grate cooler during commissioning, and insist on a long time and small flow rate, so as to minimize the impact of wastewater on the grate cooler. In addition, pay attention to regularly checking whether the waste water spray gun is blocked during operation.

The flue gas system, gypsum dehydration system and accident slurry system are the same as the power plant wet desulfurization system, so I won’t repeat them here.

3 System linkage

Before the system is running in the hot state, the system should be linked in the cold state first. Before linkage, each instrument should be calibrated, the level gauge of the absorption tower and each tank, the density meter of the absorption tower and the headbox, and the pH meter of the absorption tower to ensure the accuracy of each instrument measurement and provide reliable reference data for the operation of the system. In order to ensure the stable operation of the system; secondly, ensure that each tank has a sufficient liquid level, and the water injection level of the absorption tower should meet the starting requirements of the circulating pump. The purpose of linkage is to ensure the stable and safe operation of the entire equipment. Pay attention to the startup sequence of each sub-system during linkage. The general startup sequence of the desulfurization system is: process water system → absorbent preparation and supply system → absorption tower system → flue gas system → gypsum dehydration system → wastewater system → slurry emptying and accidents For the slurry system, the performance of the equipment and the system is inspected through a long period of operation, which lays a good foundation for the thermal operation of the system.

4 Thermal operation of the system

Before the hot state operation of the system, the online monitoring device for import and export flue gas should be calibrated to provide accurate environmental protection data for the normal operation of the desulfurization system in order to adjust the operation mode of the desulfurization system. Before hot operation, all systems are interlocked, especially the flue gas accident spray interlock at the inlet of the absorption tower, the backup interlock of each pump in the process water system, the interlock of each tank agitator, the interlock of the agitator of each discharge system, and the pit pump . Make good contact with the host, and do a good job of starting the desulfurization system when the system is ventilated, especially the starting time of the circulating pump, strictly control the temperature of the outlet flue gas of the absorption tower, and prevent the high temperature of the outlet flue gas from damaging the demister. When operating in a hot state, the number of circulating pumps should be adjusted according to the working conditions of the cement kiln and the environmental protection data of desulfurization exports, and save energy and reduce consumption on the premise of ensuring that the export data meets the standards. At the same time, the following parameters should be adjusted during operation.

4.1 pH adjustment

When the desulfurization system is operating normally and the cement kiln working condition is stable, change the pH value of the absorption tower, observe the change of desulfurization efficiency and the change of outlet sulfur dioxide, so as to determine the optimal pH value. Low pH is not conducive to the absorption of sulfur dioxide, but is conducive to the formation of gypsum. The high pH value is beneficial to the absorption of sulfur dioxide, but due to the incomplete reaction, the absorbent is wasted, and the formation of gypsum is inhibited, which is easy to poison the slurry. Combining the characteristics of the cement wet desulfurization system and after long-term operation experience, the pH value of the absorption tower should be maintained between 5.0 and 5.5 during operation, so as to ensure the desulfurization efficiency and the quality of gypsum.

4.2 Adjustment of density

With the operation of the system, the content of gypsum produced in the absorption tower gradually increases, and the density of the absorption tower slurry will also increase. When the density reaches a certain value, the gypsum dehydration system needs to be turned on. During operation, the density of the slurry in the absorption tower should be strictly controlled. The low slurry density of the absorption tower is conducive to the dissolution of limestone and the absorption of sulfur, while too high density will inhibit the dissolution of limestone and the absorption of sulfur, reduce the desulfurization efficiency, and cause serious problems. Paralysis of the desulfurization system. High-density slurry will not only increase the wear of the equipment, but also increase the power consumption of the equipment, but also due to the high density of gypsum oversaturation, the production of gypsum is blocked, and the dehydration system will also be affected. Therefore, the density of the absorption tower slurry should be strictly controlled during desulfurization operation, combined with the characteristics of the cement wet desulfurization system, and after long-term operation experience, it is recommended that the density be controlled at 1 080~1200 kg/m3 during operation, and it can also be adjusted appropriately according to different working conditions.

5 concluding remarks

By summarizing the precautions of the cement flue gas wet desulfurization system during the commissioning process, the purpose is to give the commissioning personnel a certain reference and guidance, so as to ensure the long-term, stable, safe and economic operation of the desulfurization system, and ensure that the environmental protection indicators meet the standards and are environmentally friendly. Make a contribution.