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Coke oven knowledge questions and answers

Coke oven knowledge questions and answers

1: Why do coke ovens need furnace protective iron parts?

Coke ovens are made of refractory bricks of various shapes. The refractory brick masonry is exposed to high temperatures for a long time. Due to temperature fluctuations in the coke oven and changes in climate conditions, the refractory brick masonry will expand and contract with heat. During the process of thermal expansion and contraction, some brick joints cannot withstand the stress generated by these contractions and expansions and will open. At this time, if some ash and waste gas leak into the combustion chamber through the cracks, objects such as graphite generated by thermal decomposition are deposited in the opened ash cracks. When the furnace body expands due to the increase in furnace temperature, the ash seams cannot be restored to their previous state. Such repeated shrinkage and expansion will cause the masonry to become loose and damaged. In addition, coke ovens are often hit by machinery such as opening and closing oven doors and pushing coke, as well as vibrations caused by the movement of coal trucks, which will also loosen and deform the coke oven masonry and lose its proper sealing, weakening the masonry structure strength. Therefore, the coke oven must be equipped with oven-protecting iron parts to exert a certain pressure on the carbonization chamber wall to tighten the refractory brick masonry so that it cannot expand freely, thereby protecting the coke oven body.

 

2: How to manage the tie bars in coke oven production?

Coke oven horizontal braces are generally made of low carbon steel with a diameter of 32mm. The upper horizontal braces are buried in the furnace top brace trench and should be able to move freely. In the production of coke ovens, the diameter of any cross-section of the horizontal braces must not be less than 75% of the original state. When the braces become thinner to a certain extent, they should be reinforced and replaced, otherwise the protective effect of the furnace iron parts on the furnace body will be affected. When replacing the upper brace, protective mechanical measures should be taken on the steel column on the focal side of the machine to prevent the upper part of the steel column from moving outward. The damaged parts of the upper horizontal braces are generally at the coal loading port and the root of the riser pipe. Because the temperature of the furnace top near the rising tube base and the coal loading port is high, and it is easy to leak, catch fire and corrode the tie bars, so these parts should be inspected and repaired frequently. The lower horizontal brace is a short brace, one end of which is connected to the furnace column through the hole reserved on the coke oven foundation platform beam. The temperature here does not change much, and the load on the braces is relatively stable, but regular inspections must be carried out to ensure that the lower horizontal braces are clean and dry to prevent corrosion. The longitudinal braces are longitudinally tightened against the walls at both ends of the coke oven to control the free expansion of the coke oven to both ends. In actual production, the longitudinal braces should be inspected frequently, and the maintenance of the coke oven roof should be strengthened to prevent the longitudinal braces from being burned due to leakage and fire and coal fire on the top.

3: How to manage springs in coke oven production?

In the production of coke ovens, the curvature of the furnace column must be measured according to the prescribed period, and the spring should be tightened and adjusted in time according to the curvature of the furnace column and the contact situation of the pressure points. Coke oven springs are divided into large and small types. Within the range of the maximum working load of the spring, the load is proportional to the compression amount. In coke oven production, the spring load must be checked and adjusted frequently, but it is incorrect to relax simply according to the spring load. Because after the coke oven has been produced for a certain period of time, the large spring will produce residual deformation, which will shorten the free height of the spring, increase the nominal size of the large spring, and reduce the actual load. If this change is not considered, the measured height of the large spring is not corrected, and the large spring is simply relaxed according to the measured height, and the amount of relaxation is not recorded or counted, and there is a lack of comparison, the result will be excessive relaxation. Artificially lowering the protective pressure on the coke oven masonry. In order to avoid the above problems, the loosening amount of the large nut should be continuously recorded and counted during coke oven production, and the loosening amount of the nut should not be greater than the expansion amount of the furnace body within any period of time. When the spring fails due to elastic fatigue during long-term use, it must be replaced immediately to ensure that the spring load is true and accurate. The upper large spring should be equipped with a protective cover to prevent it from being burned by fire and accelerating its fatigue failure.

4: How to calibrate the expansion measurement line frame of the furnace body on the coke side?

The scale of the furnace body expansion measurement wire frame on the coke side of the coke oven machine is the reference point for the furnace body expansion measurement and steel column curvature measurement. Whether it is accurate or not is directly related to the authenticity of the measured furnace expansion, so the measuring wire frame should be calibrated regularly. During calibration, a straight line perpendicular to the longitudinal centerline of the coke oven is drawn along the coke side of the machine through the top of the resistance wall to the center mark embedded in the roof of the coke oven. Place a straight wooden pole horizontally on this straight line, mark one end of the wooden pole, and make the mark coincide with the marking of the longitudinal centerline of the coke oven. Reserve a hole for the coke side walking platform of the large start-up coke oven, and mark the other end of the wooden pole according to the initial size determined by the measurement wire frame installed when the coke oven is built. And hang a vertical line along this mark to the elevation of the exhaust panel. If the vertical line coincides with the original markings of the measuring wire frame at different heights on the same side of the resistance wall, it means that the measuring wire frame and its markings are accurate. If the marking of a wire frame cannot coincide with the vertical line, the wire frame needs to be re-marked. This measurement should be performed regularly by professionals.

5: What are the main factors affecting furnace expansion, and how to measure and calculate them?

The expansion of the coke oven during the production process includes the increase in the length of the coke oven caused by the continuous transformation of the crystal form in the silica bricks, and the additional increase in the length of the coke oven caused by accidental damage to the coke oven, especially the impact of the furnace guard iron parts on the masonry. Insufficient extrusion force causes the masonry to relax, leading to the continuous growth of cracks and additional growth in the length of the coke oven. The former of the above situations is called the normal expansion of the coke oven, and the latter is called the abnormal expansion of the coke oven. Normal expansion is basically not destructive to the coke oven, and the coke oven still maintains its original integrity, tightness and structural strength; abnormal expansion is destructive to the coke oven, weakening the performance of the coke oven masonry in some aspects.

The coke oven expansion measurement points are selected at horizontal elevations such as the upper horizontal iron, lower horizontal iron, ramps and grate bricks. At the same horizontal elevation of these Huochunqing measuring points, pull the steel wires along both sides of the machine and focus. These wires are hung from a wire stand attached to the resistance wall. The four steel wires on each side should be kept in the same vertical plane and the distance from the center point of the coke oven should always be constant. As the coke oven expands, the distance from the steel wire to the front of the coke oven body also shortens, and the shortened value is the total expansion value of the coke oven body. The difference between the total expansion values of two adjacent years is the annual expansion value, and then divided by the design size of the furnace length, the annual expansion rate is obtained.

6: What are the dangers if the coke oven door is not tight?

⑴ In coking production, since the carbonization chamber is under positive pressure, loose gas in the carbonization chamber will leak out if the furnace door is not tight, affecting the recovery of coke oven gas and chemical products. At the same time, the leakage of waste gas will worsen the operating environment, burn out the iron parts protecting the furnace, cause damage to the coke oven body, and shorten the service life of the furnace body.

⑵ If the coke oven door is not tight, air will leak into the carbonization chamber and burn part of the coke due to pressure fluctuations in the gas collector at the end of coking, increasing the ash content in the coke and reducing the quality and yield of the coke. At high temperatures, local nodules will occur when ash interacts with the furnace wall, causing damage to the coke oven body.

⑶ If the coke oven door is not tight, it will cause pressure fluctuations in the carbonization chamber. The graphite in the joints of the furnace wall bricks is seriously damaged, causing the furnace walls to leak from each other, destroying the heating system of the coke oven, and making it difficult to control the temperature and pressure of the coke oven.

 

Coke oven door

7: How to ensure the tightness of the coke oven door?

Measures to ensure the tightness of coke oven doors are as follows:

⑴ A reasonable maintenance plan should be developed to perform regular maintenance on the furnace doors. Generally, all furnace doors should be inspected cyclically every 2-3 months. At the same time, it is necessary to strengthen the maintenance of furnace door repair equipment to ensure normal contact between the furnace door knife edge and the furnace door frame.

⑵ Strengthen cleaning management, carefully clean the tar residue, coke powder and other residues on the surface of the furnace door blade, furnace door frame and furnace door lining brick to ensure normal contact between the furnace door blade and the furnace door frame.

⑶ Strengthen the inspection and repair of the furnace door lining bricks to keep them in good condition to avoid local overheating of the furnace door and deformation, thereby damaging the tightness of the furnace door.

⑷ Strengthen the careful operation of coke pushing carts and coke blocking carts to prevent the tightness of the furnace door from being damaged due to improper operation.

8: How to check and replace the upper horizontal brace of the coke oven?

When inspecting the upper horizontal braces, the parts most susceptible to damage should be selected, that is, the coal loading port and the base of the riser pipe, and the inner caliper should be used for direct measurement. For horizontal braces that are seriously damaged or have a diameter less than 75% of the original diameter, they should be reinforced or replaced in time.

Before replacing the upper horizontal brace, a detailed replacement plan should be developed, and all replacement spare parts, materials, and corresponding replacement tools should be prepared. When replacing, first use steel wire ropes, hoists and other tools on the top of the furnace to tighten the steel columns on the side of the machine coke, and use channel steel to connect the steel columns on both sides of the machine coke to the adjacent steel columns to ensure that the tension springs are loosened. The steel columns on both sides of the rear focus will not tilt outward. Then pry open the cover brick of the tie bar, loosen the big spring of the tie bar, remove the old tie bar, and clean the tie bar trench. Place the new tie bars in place, install the upper large spring and adjust the spring tonnage to the specified load. Finally, remove the tensioning steel rope on the top of the furnace and the channel steel fastening steel columns on both sides of the machine coke.

9: What are the reasons for the breakage of the coke oven frame and protective plate?

⑴The materials of the furnace frame and protective plate cannot meet the requirements of long-term high temperature conditions, and may break due to thermal deformation.

⑵ The furnace body expands unevenly, causing uneven stress on the protective plate and furnace frame, resulting in excessive local stress and fracture.

⑶ The unreasonable tonnage control of the steel column springs causes uneven stress on the protective plate and furnace frame, resulting in excessive local stress and fracture.

⑷ When there is a heavy rainstorm, the protective plate and furnace frame are rapidly cooled and heated, and the internal stress suddenly increases and causes fracture.

⑸ If the furnace door or coke guide groove hits the furnace frame, the protective plate and the furnace frame will produce uneven stress and break.

10: How to replace the furnace frame?

When the coke oven frame is broken or deformed and affects the coke pushing operation of the coke oven or the tightness of the oven door knife edge, the oven frame should be replaced. Generally, a coke pushing truck or a coke blocking truck is used to replace the furnace frame. The day before the replacement, replace the fixed hook head bolts of the old furnace frame with new bolts one by one, prepare a furnace door to be placed on the spare furnace frame, and fix the upper and lower horizontal irons of the furnace door and the furnace frame hooks with clamps. Install the sealing asbestos rope at the outer and inner sealing grooves of the spare furnace frame, and wrap the asbestos rope with thin iron wire to fix it. When the coking time of the carbonization chamber corresponding to the furnace door frame number to be replaced is 3-4 hours, fix the upper and lower horizontal irons of the furnace door and the furnace frame hooks with clamps. Hook the door-removing mechanism onto the furnace door, remove all the connecting hook bolts of the old furnace frame, move the door-removing machine to remove the furnace door together with the old furnace frame, and move it to the furnace door repair station. Clean the contact surface between the protective plate and the furnace frame and the debris in the groove, remove the coke at the furnace mouth and blow it clean with an air duct. Use a door remover to remove the new furnace frame that is fixed with the furnace door and move it to the carbonization chamber to be replaced. Adjust the elevation of the furnace frame, move the door pick-up machine to align the new furnace frame, put on the connecting hook bolts and butterfly springs, and tighten the hook bolts. Remove the furnace door, apply concentrated ore powder to the contact between the furnace frame and the protective plate, then reposition the furnace door to resume normal production of the coke oven.

11: How to replace the flip seat?

When the flap seat is severely corroded or deformed causing the flap to fail to operate normally, the flap seat should be replaced. For a single gas manifold coke oven, first push out the coke corresponding to the carbonization chamber of the calling plate seat to be replaced and keep the furnace empty. For a double gas manifold coke oven, the high-pressure ammonia water on the other side can be opened at the end of coking. Then lift away the bridge tube and riser tube corresponding to the base, and cover the riser tube mouth with an iron plate. Adjust the pressure of the gas collecting pipe to 0-5Pa and keep it stable. You can use the manual adjustment flap of the gas collecting pipe for fine adjustment. Use the lifting device on the coal car to lift away the old flap seat to be replaced. At this time, the gas collecting pipe pressure must be controlled at 0-5Pa and remain stable. Clean the flap seat flange and install the new flap seat, then install the riser tube and bridge tube in sequence. After the replacement work is completed, the normal pressure of the gas collecting pipe will be restored and the normal production of the coke oven will be resumed.

Keep the gas collecting pipe pressure stable during the replacement process, especially after the old flap seat is lifted away, use a round cover plate to cover the connection flange. When cleaning the flange connecting the flap seat and the gas collecting pipe, use a copper tool to clean it and apply engine oil on the flange to prevent sparks.

12: How to replace the ∏-shaped pipe of the gas collecting pipe?

When the ∏-shaped tube of the coke oven is severely corroded and the problem cannot be solved by welding repair, the ∏-shaped tube should be replaced. Since the waste gas channel between the coke oven gas collecting pipe and the blower must be disconnected when replacing the ∏-shaped tube, the waste gas generated by coking in the coke oven cannot be pumped to the recycling workshop normally and can only be released. Therefore, before replacing the ∏-shaped tube, the coke oven discharge plan must be adjusted. Arrange 10 carbonization chambers on each side of the ∏-shaped tube to be discharged before a coking cycle. The number of furnaces should be reduced before replacement and in one shift. The coke oven should not be discharged 4 hours before replacement to reduce the amount of waste gas in the entire coke oven.

Before replacing the ∏-shaped pipe, first stop the coal car slide line and the trolley to grind the electricity of the electric circuit, remove the ammonia water pipe connected to the ∏-shaped pipe, and drop the flaps connecting the 10 carbonization chambers and the gas collecting pipe on each side of the ∏-shaped pipe. (These carbonization chambers are in the final stage of coking, and the amount of waste gas generated is already very small). Open the automatic dispersion ignition device of the gas collecting pipe to release the waste gas in the gas collecting pipe, and gradually close the large valve of the suction pipe until only ammonia water flows through the suction pipe, but the gas cannot flow, thereby reducing the full flow rate of ammonia water in the tar box. Reduce the speed of the blower according to actual production. The pressure of the gas collecting pipe is adjusted through the opening of the flap of the ignition device and the rising pipes at both ends of the coke oven to control it at 5-40Pa and try to keep it in a slightly positive pressure state.

Lift the old ∏-shaped pipe to be replaced, and use the pre-prepared sealing plate to cover the flanges of the manual doubling and automatic doubling. If there is a fire at the manual flap flange, wet sacks, yellow mud, etc. should be used to put out the fire. Clean the residue on the two flanges as soon as possible, then hoist the new ∏-shaped pipe and tighten the flange fixing bolts. Adjust the pressure of the gas collecting pipe to 100Pa by closing the riser pipe cover, open the discharge pipe in front of the large valve of the suction pipe, and close the discharge pipe after waste gas comes out. Then slowly open the large valve of the suction pipe, adjust the manual and automatic flaps to slightly positive pressure, and weld the leakage point at the flange. Install the ammonia water pipe connected to the new ∏-shaped pipe to resume normal production of the coke oven.

13: How to replace the protective plate and steel column?

The curvature of the furnace column should be maintained at an appropriate value, generally no more than 25mm, so as to ensure that the deformation of the furnace column is within the elastic range and to ensure that a certain protective pressure is exerted on the furnace body. A smaller curvature of the furnace column can protect its elasticity and avoid permanent deformation; if the curvature of the furnace column is too large, it may exceed the elastic limit and fail. Especially when the curvature of the furnace column on the coke side exceeds a certain value, it will also affect the blockage. The normal walking of the Jiao car. Furnace columns that have been severely deformed must be dealt with promptly and corrected or replaced. When the protective plate is broken or seriously deformed and affects the normal production of the coke oven, timely replacement should also be organized.

Before replacing the steel columns and protective plates, temporary tightening measures should be taken for the steel columns of the same size on the other side of the coke oven to prevent the steel columns on the other side from tilting out after the horizontal braces are detached from the steel columns. Select the coal loading time of two adjacent carbonization chambers to be about 4-6 hours, open the riser tube cover, remove the furnace door, pull out a part of the coke, and use a false wall made of steel pipes and aluminum silicate refractory fiber boards to block the coke in the carbonization chamber. . Use a coke pushing car or a coke blocking car to remove the furnace frame, slowly loosen the connection between the steel column and the upper and lower horizontal braces, and use a crane to remove the steel column and protective plate to be replaced. After the front of the combustion chamber burner is cleaned, use a crane to install the new steel columns and protective plates, adjust the tonnage of the large springs on the upper and lower horizontal braces to the specified load, and then use a coke pusher or coke blocker for installation. Nice stove frame. Normal production of the coke oven can be resumed after the sealing work on the furnace head is completed.

If the steel columns and protective plates are to be replaced for the whole furnace, the coke oven temperature and coke pushing plan should be carefully arranged and accurately adjusted. The replacement can be done during the day and the coke oven production can be resumed at night. However, high temperature accidents must be prevented. , and at the same time, it is necessary to prevent difficulties in pushing coke due to insufficient maturity of the coke oven.

14: What is the significance of measuring the inclination of the riser?

The bottom of the coke oven riser tube is connected to the furnace top riser tube seat, and the upper part is connected to the socket of the gas collector flap seat through the bridge tube. The gas collector is located on the upper part of the steel column. Therefore, the inclination of the riser can, to a certain extent, reflect the deformation of the upper part of the steel column and the outward movement and deformation of the gas collecting pipe. When measuring the inclination of the riser tube, you can fix the end of the vertical line on the pallet, hold the pallet against the upper part of the riser tube, measure the distance between the lower part of the riser tube and the vertical line, and then calculate the inclination of the riser tube. The inclination of the rising tube measured each time should be recorded and carefully compared and analyzed.

15: What is the significance of measuring the verticality of a resisting wall?

During the oven and production process, the coke oven will expand in the length direction of the entire coke oven, causing the frame-type resistance wall to tilt. Therefore, the verticality of the resistance wall can reflect the deformation degree of the coke oven in the length direction to a certain extent. and stress conditions, and can also reflect the working conditions of the coke oven longitudinal braces. When measuring the verticality of the resistance wall, open the measuring hole covers on the second-floor furnace platform and the furnace end platform of the coke oven, and measure the distance from the vertical line to the vertical line from the upper, middle, and lower points of the resistance wall. Then calculate the verticality of each section of the resisting wall. If there is no measuring hole for the second-floor furnace platform or furnace end platform, use the hanging vertical line method to measure the verticality of the height from the upper part of the resisting wall to the second-floor platform. The verticality of the resistance wall measured each time should be recorded, and the measurement data should be compared and analyzed. If there is a large difference between the two measurement data, the measurement should be repeated and the reasons should be identified.

16 How does coal turn into coke in the carbonization chamber?

The cohesive blended coal is transformed into coke in the carbonization chamber of the coke oven. It generally goes through three stages: drying and desorption, semi-coke shrinkage and coke formation. These three stages are intertwined with each other and cannot be completely separated.

The first stage is from normal temperature to 300℃, which is the drying and degassing stage of coal. Before normal temperature reaches 120°C, coal mainly undergoes dehydration and drying; at 120-200°C, coal releases adsorbed gases such as CH4, CO2, CO, and N2, which is a desorption process; at 200-300°C, coal begins to decompose and generate CO2, CO, H2 and other gases simultaneously release crystal water and trace amounts of tar.

The second stage is from 300-500℃, which is the semi-coke formation stage dominated by depolymerization. At 300-450°C, coal undergoes violent decomposition and depolymerization, precipitating a large amount of tar and gas. The gases are mainly CH4 and its homologues, as well as H2, CO2, CO and unsaturated gases. These gases are primary pyrolysis gases, during which a colloid is formed into three phases of gas, liquid and solid. It causes coal to soften, melt, flow and expand; within the temperature range of 450-500°C, the colloid decomposes, condenses and solidifies into semi-coke.

The third stage is from 550-1050℃, which is the coke formation stage based on condensation polymerization. At 550-750℃, semi-coke decomposes a large amount of gas, mainly H2 and a small amount of CH4. These gases are called pyrolysis secondary gases. During this period, as the temperature increases and the gases precipitate, cracks will form in the semi-coke. At 750-1050°C, the semi-coke further condenses and continues to precipitate a small amount of gas, mainly H2. The decomposed residues are further condensed, the coke becomes tight and hard, the arrangement tends to be regular, and the semi-coke is transformed into coke with a certain strength and blockiness.

17: How does raw gas flow and cool during the coking process?

Raw gas export equipment includes rising pipes, gas collecting pipes, suction pipes and corresponding ammonia spraying systems. It is used to cool and export the raw gas from the furnace, maintain and control the positive pressure of the carbonization chamber during the coking process, and prevent the carbonization chamber from being too high and leaking gas to pollute the environment. The raw gas with a temperature of about 700-750℃ is led out from the riser pipe. When flowing through the bridge pipe, it is cooled by spraying thermal cycle ammonia water with a temperature of 75-80℃. Due to the rapid evaporation of part of the ammonia, a large amount of heat is absorbed, causing the temperature of the raw gas to drop sharply to 80-90°C. At the same time, about 60% of the tar vapor in the gas condenses and precipitates. The cooled gas, circulating hot ammonia water and condensed tar enter the gas collecting pipe together, and flow along the gas collecting pipe in the direction of the suction pipe in the middle of the gas collecting pipe. The gas flows in the upper part of the gas collecting pipe section, and enters the suction pipe through the ∏-shaped pipe; low-pressure ammonia and tar flow in the lower part of the gas collecting pipe section, and passes through the tar box (maintain a certain liquid seal height to prevent waste gas from passing through ) into the suction pipe. The suction elbow (∏-shaped tube) is equipped with an adjustment flap to control the pressure of the gas collecting pipe, so that the pressure at the bottom of the carbonization chamber under the suction pipe is maintained at 5Pa before coke pushing. The raw coal gas, circulating ammonia water and condensed tar in the suction pipe flow together to the gas purification process. After passing through the gas-liquid separator, the gas enters the primary cooler for further cooling. The circulating ammonia water and condensed tar enter the tar ammonia water clarification tank to separate the tar residue, tar and circulating ammonia water. After the circulating ammonia water is replenished with evaporation, the circulating ammonia water pump is sent back to the coke oven to spray and cool the raw coal gas.

18: How to judge the maturity of the coke cake in the carbonization chamber before coking?

Under normal circumstances, before taking off the oven door and pushing the coke, the coke cake in the carbonization chamber is in a mature state at the end of coking. If the coke is not mature enough or the coke is overcooked, it means there is a problem in some part of the coking process. The maturity of the coke cake can be judged from the status of the rising tube flame, the furnace top space flame, and the coke cake in the carbonization chamber.

⑴The coke cake is in a mature and good state. The flame in the rising tube is about 1m high, golden yellow, clear and thin, in the shape of a cloud, and without black smoke. The coke cake in the carbonization chamber is golden yellow, and the coke cake shrinks well, with a shrinkage gap of about 10-15mm. The flame in the top space of the furnace is clear, thin, without thick smoke, and shines silvery white into the eye.

⑵The coke cake is not mature enough. The flame in the rising tube is purple-red, with black flame included, and the flame fluctuates up and down.

 

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