About the introduction of the torch system of Qingdao Refining & Chemical Company

1.1 Process

The refinery system of Qingdao Refining & Chemical Company is divided into three pipe networks, corresponding to three torch heads. The high-pressure venting pipe network (DN1000) alone corresponds to a set of liquid separation tanks, water-sealed tanks and 1# main flare heads, and receives air release bodies from the hydrotreating reaction section, the gas fractionation apparatus and the hydrogen pipe network pressure control. The low-pressure venting pipe network (consisting of one DN1400 and one DN1100 pipeline in front of the liquid separation tank) corresponds to one set of liquid separation tank, water sealing tank and 2# main flare head, accepting 14 sets of process equipments other than the above, storage and transportation System, fuel gas pressure control, etc.; the DN1100 line receives the venting gas from the catalytic cracking and coking unit. The acid gas torch is a separate system, corresponding to the acid gas water seal liquid separation tank and the 3# torch head, and accepts the sulphur combination device to discharge the acid gas in an emergency.

Before entering the liquid separation tank, the high-pressure venting system leads out a DN700 branch line through valve 2, and valve 3 enters the 20000m3 gas cabinet for flare gas recovery; before the two lines of the low-pressure venting system enter the liquid separation tank, each DN700 branch line is drawn, after confluence Through valve 1, valve 3 enters the 20000 m3 gas cabinet for flare gas recovery. In order to prevent the negative pressure of the venting system pipe network, the design is to take out the venting pipe network pressure-retaining line (DN 150) from the flare gas compressor outlet line (DN200), and pass the valve 4 before the high- and low-pressure venting line enters the flare gas condensate tank. The valve 5 is pressurized to ensure that the pressure of the pipe network of the two venting systems is not less than 2 kPa. In normal production, the flare gas recovery system is activated, and the water sealing height of the water sealing tank of the high and low pressure venting system is 1000 mm, and the torch is extinguished. The gas discharged from the normal discharge of the device or leaking inside the valve enters the gas cabinet, is compressed by the compressor to 1.1 MPa, and then sent to the dry gas desulfurization device. In the state of start-stop or accident of the device, the water-sealed tank drain sealing valve group is interlocked open, the water seal height is reduced to 400mm of the fixed water seal, and the valve 1 or valve 2 is interlocked, and the high-altitude automatic ignition system is started to ignite the torch long lamp. To achieve safe discharge of air release body. When the pressure and temperature detection signals meet the normal operating conditions, the water seal height is increased again to 1000 mm, and the flare gas recovery is started.

1.2 Torch Overview

The company has a total of 3 torches, 2 DN1400 main torches, 1 DN700 acid torch, and 150m high torch. It is laid for bundled common towers. The tower structure is fully welded. The torch head is equipped with a repairing platform at the top of the torch tower.

1#, 2# The lower part of the torch head is equipped with a fluid sealing device; the torch is equipped with a smoke suppression system; the torch is equipped with 12 sets of high-altitude igniters, 1 set of ground igniters and 12 sets of long-lighting lamps; the power of the torch facilities is uniformly supplied from outside the boundary area; The system can be operated on site by the I/O station and the central control room DCS outside the precinct.

2 reduce flare gas emissions

2.1 Realize the orderly discharge of the flare gas of the device. The key to the torch is to pick up the light from the source and control the gas discharge of the device. Qingdao Refining & Chemical Company optimized the operation of the whole plant and basically realized the goal of controlling the whole plant flare gas emission of 3000~3500m3 / h and the flare compressor (recycling capacity of 1800m3 /.). The production schedule timely grasps the flare gas discharge of each device, monitors the valve opening time on the DCS for the possible discharge valve, strengthens the composition analysis of the flare gas, and timely checks the device that may discharge the gas to realize the flare gas of the device. Orderly discharge. For example, the composition of the flare gas on a certain day is shown in Table 2. According to the analysis results, the leakage of the safety valve of the hydrogenation unit is quickly determined. After the measures are taken, the amount of venting is reduced by about 800 m3 / h. 2.2 The process of optimizing the gas discharge of the device may not be in some devices. The gas optimization process that is discharged into the flare system is directly utilized to reduce the flare gas flow from the source. For example, the continuous reforming unit is degassed from the top of the isopentane column gas to the hydrogen conversion converter to reduce the flare gas by about 350 m3 / h; the solvent regeneration device flash gas is changed from the torch to the direct The incinerator burns and reduces the flare gas by about 180m3 / h.

2.3 Do a good job of fuel gas, hydrogen system balance optimization of the whole plant fuel gas pipe network, hydrogen pipe network operation, do a good job of fuel gas, hydrogen balance, eliminate pipe network fuel gas, hydrogen to the flare system vent, reduce the load of the flare gas recovery system. Fuel gas balance is one of the difficulties in refinery production. The company's actual processing of crude oil is heavier than designing crude oil, and the fuel gas output is large. The production is mainly used to adjust the start-up boiler load, adjust the catalytic, coking unit treatment capacity, adjust the catalytic unit reaction temperature, etc. Means to achieve fuel gas balance.

Hydrogen balance is achieved by timely adjusting the hydrogen production, reforming, hydrotreating, diesel hydrogenation and other hydrogen production equipment loads.

3 Improve the safety of torch emissions

3.1 Setting Reliable Process Interlocking In order to ensure that the device accident state is largely emptied, the torch system can safely ignite the air release body and protect the gas cabinet in time. The company has scientifically and rationally set the process interlock of the torch system. The interlocking conditions and interlocking action relationship of the torch system are shown in Table 3.

3.2 Improve the reliability of the ignition system

a) Solve the problem of fuel gas and liquid. Torch light, the fuel gas used in the high-altitude igniter is the end of the fuel pipe network of the whole plant, and the fuel gas consumption is small. Therefore, the fuel gas in the torch part is more serious, which affects the success rate of ignition. According to the site situation, before adding a DN15 crossover to the torch separation tank at the bottom of the fuel gas filter, keep the over-line valve open 1/3, so that the fuel gas enters the torch separation tank, effectively solving the fuel gas. The problem of liquid belting improves the success rate of ignition.

b) Solve the problem of moisture in the high voltage generator. At the beginning of the construction, the high-altitude igniter of the torch occurred many times because the high-voltage generator was unable to catch fire and was not ignited. A well-sealed moisture-proof box is added outside each high-voltage generator to ensure the normal operation of the high-voltage generator.

c) Regular trial operation of the ignition system. It is stipulated that all long-lighting lamps should be piloted every night shift, and the problems found should be recorded, and the success rate of ignition should be more than 80%.

d) Regularly carry out the fuel gas pipeline through and purge. Every week, the long-lighting, high-altitude igniter and explosion tube are blown once with steam or nitrogen to ensure smooth pipeline and improve ignition reliability.

3.3 Ensure that the torch head is safe for the safety of the torch head. For long-term operation, the following two points must be guaranteed.

a) When recovering the flare gas, ensure that the fluid seal nitrogen is sufficient and continuous to prevent the explosion from reaching the explosion limit after the air enters the torch cylinder and the combustible gas. After the open flame, flashing occurs at the torch head, affecting the long period of the torch head. run. According to the relevant standards, the flow rate of the purge gas should be such that the oxygen content at 7.6 m from the top of the torch cylinder does not exceed 6% (volume fraction) when the alkane is discharged, and does not exceed 3% (volume fraction) when the hydrogen is discharged. For molecular seals or fluid seals for overhead flare systems, the purge gas is typically required to have an upward gas flow rate of no less than 0.03 to 0.06 m/s at the flare exit. Considering the high winds at the seaside and the high hydrogen content of the air release gas, the purge gas velocity is 0.06 m/s, and the minimum nitrogen volume required for each flare head fluid seal is 332.3 m3 / h to effectively prevent air from entering the flare cylinder.

b) When the flare gas is vented, ensure sufficient steam, smoke exhaust and central steam to prevent damage caused by excessive temperature of the torch head. When the amount of venting is small (<3×103 m3 /h) and the hydrogen content in the air release body is high, it is necessary to pay attention to opening up the steam flow to prevent the torch head from being damaged due to "burning".

4 guarantee sufficient recovery capacity

4.1 Strengthening the torch generator design of the torch compressor The normal recovery amount is 3600m3 / h, the maximum recovery is 5400m3 / h, the capacity is 20,000m3 dry gas cabinet, and the two-stage compression with the suction capacity of 1800m3 / h is configured. 3 sets of screw compressors. Due to problems such as unclean media and quality of compressor manufacturing, it is difficult to operate and maintain the compressor. Strengthen the five-in-one special management of the "machine, electricity, instrument, tube, and operation" of the compressor, so that the integrity rate of the torch compressor reaches 81%. According to statistics, the company's flare gas compressor has been in operation for 8 months. Recycling gas venting 1.73×104 t, reducing the overall processing loss of the whole plant by about 0.31%.

4.2 Recycling flare gas using system flow

a) The flare gas is recovered by the normal top compressor through the compressor inlet flare line, and the recovery amount is about 1500 m3 / h, which is equivalent to increasing the recovery capacity of the gas cabinet compressor. The venting line of the atmospheric and vacuum distillation unit enters the low-pressure venting system. In order to prevent the venting of the venting system caused by the negative pressure of the venting system, the torch tempering occurs. This process is used to recover the gas inlet valve and the main valve of the gas cabinet. Fully open, 2# torch water sealing tank water seal height ≥ 600mm.

b) In combination with the current status of the flare compressor, the flow between the pressure device stage of the catalytic converter and the air compressor stage of the coking unit is added to the exit line of the torch compressor. As a special case, the flare gas is recovered to ensure the long-cycle operation of the torch compressor. Alternate means.

4.3 Addition of flare gas compressor The flare compressor should have relatively sufficient recovery capacity, which will enhance the operational flexibility of the flare gas recovery device and fundamentally solve the gas balance problem of the whole plant. After investigation, we chose a set of two series operation screw compressors with a flow rate of 3,877 m3 / h and an outlet pressure of 1.1 MPa to meet the production needs.

5 problems and countermeasures

5.1 Water seal tank structure defects

In order to prevent tempering of the torch, it is recommended that the water sealing tank be modified to the following options.

a) Increase the volume of the water-sealed tank, or connect a new water-sealed tank in parallel with each water-sealed tank on an existing basis. And reduce the fixed water seal height to 200 ~ 300mm, while ensuring sufficient effective water seal, while reducing the noise of the torch discharge.

b) Increase the water replenishment capacity of the water sealing tank replenishing valve group. According to the on-site operation, it is recommended that the water supply line be changed to the water supply valve DN100 and the water supply auxiliary line valve DN40. The two lines are equipped with control valves for remote control.

c) Practice shows that when the gas is vented in a large amount, the water in the water seal side of the water-sealed tank is all taken to the settlement side, and the water discharge is sealed through the sedimentation side. At this time, if the upstream device is in extreme working conditions, such as the emergency pressure relief of the hydrogenation device, and the pressure relief valve is suddenly closed, there is no effective water seal on the water seal side, which may cause a tempering accident. It is recommended to raise the water-sealing tank to the side of the tank to drain the U-tube, and lift the top of the U-tube to 1.5m above the bottom of the tank. Keep the withdrawal valve normally open during the discharge process, so that when the above extreme conditions occur, the water The water stored on the settlement side of the sealed tank can be pressed back to the water seal side through the withdrawal valve, and an effective water seal can be quickly established to meet the requirement that the water inlet height of the torch inlet pipe is greater than 3 m under any working condition.

5.2 Hydrogenation unit emergency pressure relief

For the flare system, the emergency pressure relief of hydrotreating and diesel hydrogenation units is an extreme condition. Its main feature is that the hydrogen content in the air release body is high (volume fraction >90%), the venting amount is large, and the valve is suddenly closed when the discharge is stopped (the valve closing time is about 20 s), which easily causes a tempering accident in the flare system. In order to ensure the safe operation of the flare system during the emergency pressure relief of the hydrogenation unit, it is recommended that: 1 The emergency pressure relief situation of the hydrogenation unit should be started by first opening the pressure line of the flare system for pressure compensation, and before shutting down the emergency pressure relief valve, Open the discharge control valve of the hydrogenation unit to make pressure, and the negative pressure of the fire-retardant venting system will cause tempering; 2 change the emergency relief valve of the hydrogenation unit to the quick-opening type to prevent sudden closing of the valve. The phenomenon of air hammer causes tempering caused by negative pressure on the pipe network.

5.3 production device without flare gas flowmeter

In order to further grasp the discharge situation of the flare gas of each production device in time, the order of the flare gas emission of the device is realized in an orderly manner, and problems are dealt with in a timely manner. It is recommended to add a flare gas discharge flowmeter to each production device, and the production schedule checks the discharge of the flare gas. , assessment. According to the relevant introduction, ultrasonic flowmeter should be selected on the flare gas pipeline.

5.4 Torch head "焖烧"

It is recommended to draw a DN350 ~ DN500 line between the high and low pressure torch water seal tank and the liquid separation tank, before the acid gas torch (DN700) water seal tank. In this way, when the high and low pressure torches are vented at a small flow rate (<3×103 m3 /h), the new air line is used to put the air release body into the acid gas torch for combustion to prevent the small flow gas from burning on the large torch head. Burning phenomenon, prolonging the service life of the torch head. At the same time, the setting of the interlocking logic of the venting system after the process transformation should be fully considered.

5.5 compressor inlet filter is frequently blocked

According to statistics, in the past 8 months, the compressor inlet filter has been shut down for 31 times, which brings great difficulties to safe production and long-term operation of the compressor. It is recommended to take the following measures: 1 Purify the torch gas of the coke unit; 2 Check the filter at the gas inlet to ensure the gas entering the gas cabinet is clean; 3 Reform the compressor inlet filter, on the one hand 2 filters, 1 open and 1 standby, to achieve online cleaning; on the other hand, increase the filtration area from 0.3m2 to 10m2. 6 Conclusion After continuous exploration and improvement, Qingdao Refining & Chemical Company torch ignition system, interlocking system, The recovery system is stable and reliable, and the accident discharge is safe and reliable. All the normal production is recovered, and the goal of "eliminating the high and low pressure torch long light, the whole plant gas emission is less than 3500m3 / h" is achieved. Does this save the company about 2.8×106 kW? h/a, saving about 24,000t/a of steam, reducing the overall processing loss of the whole plant by about 0.31%, and extending the service life of the flare head. The optimized operation of the torch system indicates that the company's production management has reached a high level, which is of great significance to the company's sustainable development.

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