Analysis and countermeasures of explosion and explosion accident in cement plant

Date: 2019-08-19 Views:

With the continuous progress of cement production technology, the new dry kiln has been widely recognized and promoted by the cement industry for its advantages of energy saving and environmental protection, good clinker quality, large production, low investment cost, high operation rate and stable operation.

In recent years, the annual NSP kiln growing at a rapid rate, due to technical and management personnel growth does not synchronize with NSP kiln development, frequent accident of NSP kiln combustion process, production and equipment damage, appear even the personnel casualty, causes big economic loss to the enterprise, especially in winter, is the NSP kiln combustion process of the accident Tuesday.In this paper, several combustion and explosion accidents in the production of new dry kiln are analyzed, and preventive measures are made to prevent similar accidents from happening again.

cement plant

1.Combustion accident of coal mill electric precipitator


In the winter of 2006, the continuous rain and snow caused the wet raw coal and other materials in the open storage yard of plant A.Due to the moisture of raw coal, not only the coal mill production is greatly reduced, the coal powder supply is tight, but also the smoke humidity of the coal mill dust collector increases, causing the coal mill dust collector dew, dust bucket blocking.Before the accident, the central control operator found that the second electric field voltage of the coal mill dust collector was low, and then arranged to stop the machine for inspection. After opening the inspection door of the coal mill dust collector, it was found that the coal powder in the electric field had been burned, a large amount of smoke appeared in the electric field, and the surface coal powder in the ash bucket had Mars, and the temperature was higher.Then organize personnel to deal with the aftermath of the accident, and do a good job to stop the kiln preparation work.The accident not only caused the suspension of kilns for 31 hours and the loss of more than 20 tons of pulverized coal, but also caused serious environmental pollution.
 

1.1 accident handling


(1) immediately stop the coal mill system after the accident, stop the fan of the coal mill electric dust collector, and close the inspection door of the coal mill electric dust collector.Because fire area is small, do not need to open the CO2 fire extinguishing system, open the supply channel, the screw conveyor under electrical precipitator ash hopper by inversion, makes the pulverized coal ash hopper in electrostatic precipitators discharge from ash discharge passage to the outside of the mill, at the same time with fire water bag to get rid of pulverized coal burning in a timely manner sprinkler, prevent secondary combustion, until the pulverized coal ash hopper in the row.

(2) at the same time, check the coal bunker.Since the coal powder warehouse did not catch fire, it is required to use up the coal powder warehouse as soon as possible and make preparations to stop the kiln.

(3) for the discharge of coal dust, in addition to the site sprinkler, also send someone on duty to watch, to prevent resurgence.After normal production, organize personnel to clean up pulverized coal and clean up the site environment.

 

1.2 cause analysis


(1) the coal mill electric dust collector is one of the main process equipment of the coal mill system, whose function is to collect the finished coal dust.When the ash bucket appears to block, the coal into the coal powder bin volume will drop significantly, the coal powder bin hole depth changes greatly.It is easy to judge whether the dust bucket of coal mill dust collector is blocked or not according to the abnormal change of hole depth of coal dust bin.Before the accident, the central control operator and inspection personnel did not make judgment in time, so they could not take measures in time, leaving hidden dangers for the accident.

(2) because the coal mill dust collector of the cement plant is of 2 electric field and 4 dust bucket structure, before the accident, the first electric field works normally, and the second electric field clogs the dust bucket due to condensation, at this time, the amount of coal into the coal bunker drops.Due to the wet raw coal, the coal mill production dropped significantly, coal powder bin level is low.In order to avoid stopping the kiln, managers and operators subjectively want to fill the coal bunker as soon as possible and then stop the process.With the clogging of the ash bucket, the coal mill system has entered into a vicious cycle, which creates conditions for the further accumulation of coal powder in the ash bucket.

(3) after the accumulation of coal dust in the dust bucket of the second electric field of the electric precipitator to a certain extent, it begins to affect the operation of the electric precipitator. The secondary voltage of the second electric field of the electric precipitator drops, and dust emission at the outlet increases.If this time stop processing, the accident can be avoided;However, due to the insufficient understanding of the possibility and severity of the fire and explosion accident, the management continued to start production, which eventually led to the occurrence of the accident.

 

1.3 improvement measures


(1) revise the operation rules of coal mill and electric precipitator, including the management of preventing coal powder from burning and exploding, organize the management personnel and operators of coal mill fire management knowledge training as soon as possible, improve the safety awareness of preventing coal powder from burning and exploding.

(2) the inspection personnel are required to check the discharging situation of dust bucket of electric dust collector and coal dust bin every hour, especially in the rain and snow weather, and immediately organize cleaning to prevent the accumulation of coal dust in the coal mill electric dust collector.

(3) check the fire fighting system of coal mill regularly, replace CO2 leaking cylinders and expired fire extinguishers in time, and take timely measures in case of accidents to ensure the safety of coal mill production.

cement plant

2.Shooting accident in decomposing furnace


In the winter of 2005, the 1 500 t/d clinker production line of plant B temporarily stopped the kiln for about 8 hours and adopted diesel heating to increase the temperature. After the temperature was increased for about 3 hours, the temperature meter of kiln tail showed that the temperature of coal spraying had reached the temperature of coal spraying.Afterwards, the kiln was stopped for inspection, and no abnormality was found, so diesel fuel was used again for ignition and heating up. When the temperature meter at the end of the kiln showed that the temperature had reached the temperature of coal injection, coal injection was carried out on the decomposing furnace. A few minutes later, shooting occurred again in the decomposing furnace.
 

2.1 cause analysis


(1) as a temporary stop kiln, its heating time is determined by the temperature inside the kiln and the environment temperature, which cannot be operated by experience.The main reason for the accident is that the post staff only paid attention to the temperature of the kiln end meter.Due to the focus of the enterprise on the production of clinker, quality and raw fuel material consumption and wage linked to the assessment, the central control operator thought early ignition, more production of clinker, but also can reduce diesel consumption, the starting point is good, but did not achieve the expected effect.

(2) from the perspective of the phenomenon of inner blasting, the reason is that the CO concentration exceeds the standard. The CO concentration in the kiln tail cannot be measured by the CO analyzer due to the closure of the air door of the kiln tail fan when the kiln is heating up, and the monitoring function is lost.

(3) since it was the early winter, the ambient temperature was relatively low. Although the meter temperature of the kiln tail reached the requirement of coal spraying after heating with diesel oil, the actual temperature in the kiln and the material field of the decomposing furnace did not reach the expected temperature, and the temperature display was only local temperature.Caused by furnace heating time is too short, decomposition furnace and furnace heat storage, low temperature field, the pulverized coal injection, after decomposing furnace for pulverized coal can't in decomposition furnace full combustion, decomposition furnace temperature not only didn't rise, fall instead, no combustion of pulverized coal to produce a large amount of CO gathered in the stove, decomposition furnace containing O2 drops, with the decomposition of pulverized coal and air entering the furnace increase (O2), when the concentration of CO, gathered to a certain degree, after shooting in phenomenon.

 

2.2 preventive measures


According to the above analysis, the main cause of the problem is the insufficient heat storage of the material temperature field in the decomposition furnace.When ignition and temperature rise again, increase the temperature with diesel oil by 2 h (oil and coal mixed injection time) on the original basis, and then spray coal on the decomposition furnace, the rotary kiln runs normally.In order to prevent the recurrence of similar accidents, the following rectification measures are proposed:

(1) periodically calibrate the temperature control points of the rotary kiln to ensure accuracy and effectiveness, and prevent errors in judgment of the central control operators caused by instrument errors.

(2) the control of the heating time of rotary kiln shall be comprehensively considered according to the stopping time of kiln, the temperature inside the kiln and the environment temperature. The key point shall be to understand the actual temperature in the kiln and the material field inside the decomposition furnace, and then consider when to spray coal to prevent the explosion accident caused by insufficient temperature in the material field.

(3) according to the cause of the wrong operation of the accident, modify and improve the operation procedures of the central control, organize training and examination for the workers of the central control, improve the operation level and prevent the recurrence of similar accidents.

 

3. Summary


With the upsizing of cement production equipment, labor productivity has been increasing, and most posts have been replaced by patrol inspectors. Patrol inspectors' duty scope has been expanded, and their business knowledge requirements have been raised.According to years of investigation and statistics, most of the combustion and explosion accidents occurred in the production process of new dry method production line are caused by imperfect operating procedures and insufficient training of operators, which makes the staff have a deviation in understanding operating procedures.Therefore, it is very important to improve the operating rules of the post and strengthen the business training and examination of the operating staff, especially in the newly built cement enterprise, so that the staff can get familiar with the operating rules as soon as possible.

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