Coke oven construction, oven baking and start-up(3)

Section 2 Coke oven installation

1. Preparation for furnace construction

The preparation for furnace construction involves many aspects. First of all, the organization of construction should be done well, including: construction plan layout, construction progress, labor organization and construction methods. In order to ensure the quality of brickwork, a quality inspection agency should be established. During the entire construction process, full-time inspections should be carried out to ensure the quality of construction.

1 Requirements for brickwork greenhouses and storage of refractory materials

The masonry of coke ovens should be carried out in greenhouses. The greenhouse should be windproof and rainproof to ensure the stability of the waterline, prevent rain from eroding the mortar joints, prevent the masonry from getting damp and the poles from deforming. The temperature in the greenhouse should be higher than 5℃ in winter to prevent the mud from freezing, and there should be sufficient and uniform lighting.

The refractory materials coming to the factory should be verified and accepted. When entering the warehouse, they should be marked and stacked separately according to the order of use and tolerance of the brickwork parts. Refractory materials should be placed in the warehouse. The brick warehouse should be able to prevent rain and snow, the floor should be solid to prevent sinking, and there should be drainage ditches around. The ash storage should be strictly protected from wind and rain to avoid blowing away fine-grained fire mud, mixing with mud and sand, and agglomeration due to moisture.

2 Pre-laying

Due to the complex shape of coke oven bricks and the large amount of bricks, in order to ensure quality and avoid rework, the brick layers of representative parts such as heat storage chambers, ramps, and carbonization chambers and complex parts of the furnace roof must be pre-laid before construction to check whether the appearance of refractory bricks can meet the quality requirements of masonry, so as to provide a basis for the processing of refractory bricks and the use of large and small tolerances, check the bricklaying performance of refractory mud, and determine the configuration plan of mud materials; review the design drawings and the manufacture of refractory bricks for errors. Technical workers should also be trained to master the technology.

3 Laying the foundation of the furnace and plastering the resistance wall

The coke oven is built on the top plate of the foundation, and the surface of the top plate is required to be flat and uniform. Before bricklaying, the surface of the top plate should be smoothed with cement mortar until it reaches the design elevation. The elevation tolerance of the top surface after the red bricks are laid should be within the allowable range.

For the bottom-spraying coke oven, the bottom spray pipe should be buried before plastering. The lower nozzle of the coke oven is connected to the brick gas channel of the furnace body. Since the expansion of the coke oven masonry and the foundation from cold to hot is different, the center distance of the lower nozzle is different from the center distance of the cold brick gas channel to adapt to the change of the position of the brick gas channel after the furnace body expands. The center distance of the lower nozzle specified in the design is greater than the center distance of the cold brick gas channel, and varies with the material of the heat storage chamber.

For example: the center distance of the vertical fire channel is 480mm, the silicon brick heat storage chamber is calculated according to the expansion of 1%, the center distance of the lower nozzle is 484mm, the clay brick is considered according to the expansion of 0.5%, and the center distance of the lower nozzle is 482mm. During construction, their tolerances are required to be ±3mm. Otherwise, the error is too large, or brickwork cannot be laid, or the lower nozzle and the brick gas channel do not overlap after the furnace is baked, and even the pipe bricks are cracked.

During the furnace baking process, the resistance wall and the furnace body have relative displacement. Therefore, the contact part between the resistance wall and the furnace body is a sliding surface, and cement mortar should be used to smooth the resistance wall. Its control tolerance and straightness are 5mm, and its verticality is also 5mm.

4 Reference line for furnace construction

The coke oven is a relatively complex industrial heating furnace. The relevant dimensions between the furnace body itself and other equipment and machinery are relatively strict. Therefore, the linear dimensions of each part and each furnace hole should be strictly controlled. Otherwise, it will affect the quality of the project and cause great waste. For this reason, permanent stakes and reference points should be buried before construction, nails should be buried, and horizontal marking plates and vertical marking poles should be set.

(1) Permanent stakes and reference points are used to control the overall size of the coke oven

The longitudinal center line of the coke oven is the main control line for the position of the coke oven group. Permanent stakes are buried on the resisting wall, coal tower or the site outside the furnace end platform of the coke oven. The permanent stakes of the side furnace are the center lines of the carbonization chambers at both ends of the coke oven, which are used to control the entire length of the coke oven and are strictly perpendicular to the longitudinal center line. The reference points are used to control the horizontal elevation of various parts of the furnace body. Generally, one stake is buried on one side of the furnace group, or one stake is buried on each side. A spare reference point can also be buried at the coal tower.

(2) Installing nails Permanent stakes and reference points are installed outside the greenhouse. For the convenience of bricklaying, permanent stakes and reference points are led to the resisting wall and the top plate of the foundation, and a certain number of nails are installed. The center points are engraved on the nails for the purpose of pulling the center line of the longitudinal axis and the two parallel front limits when laying bricks.

(3) Installing horizontal mark plates and vertical mark rods The horizontal mark rods are used to control the center line of each furnace wall masonry. The position of the center line of each combustion chamber is indicated by wood screws on the mark plate. The vertical mark rods are used to control the elevation of each layer of bricks. One is installed every other combustion chamber (installed at the same time as the horizontal mark plate).

5 Preparation of mud materials

Mud materials have a great influence on the quality of bricklaying. The properties, characteristics and quality requirements of various fire muds are described in the first section. Mud materials should be used as soon as they are prepared and should not be stored overnight; the mud materials used in different parts of the masonry are different and must not be mixed; the quality of the refractory mud entering the factory must be tested to ensure that the refractoriness and combination meet the requirements. When finished fire clay cannot be supplied or the fire clay varieties are incomplete, it is necessary to prepare it on site according to the requirements of each masonry for refractory clay. The proportion of the mud can first be estimated by the composition analysis data of the raw material or other types of fire clay (mainly the content of SiO2, and the content of Al2O3 for clay fire clay) and the required content of the fire clay. Then, the refractoriness of fire clays with different proportions is tested, and the proportion that meets the requirements is selected to prepare the mud. During preparation, the mud must be mixed evenly, and the equipment used should prevent uneven mixing due to the agglomeration of raw clay. The prepared fire clay should be tested batch by batch and can only be used after passing the test. Raw clay has a large hygroscopicity, while quartz powder has a small hygroscopicity. When using them to prepare silicon fire clay, the moisture content of the raw materials should be analyzed during preparation and converted into dry basis moisture to ensure the accuracy of the proportion.

2. Furnace Masonry

1 Quality Requirements for Coke Oven Masonry

(1) Brick Joints. Coke oven masonry is built with a single piece of refractory mud. Refractory mud is generally not easy to be well sintered in the lower part of the furnace body where the temperature is low. Although it is sintered in the upper part of the furnace body, its strength is not high, so the brick joints become the weak link of the masonry. In order to increase the tightness of the coke oven masonry, although a lot of special-shaped bricks are used, the brick joints must still be full and tight. The brick joints should not be too wide, otherwise the strength and tightness of the masonry will be deteriorated, but they should not be too narrow, otherwise the mortar joints should not be full and difficult to groove, which is easy to cause empty joints and reduce the strength of the masonry. According to practice, the mortar joints of 3~6mm are more suitable, which can not only achieve full mortar joints during masonry, but also meet the requirements of production technology. In order to achieve full brick joints, the coke oven bricklaying should adopt the "squeeze method", that is, put mortar on the masonry, apply mortar on the bricks to be laid, and then lay the bricks along the mortar layer to the appropriate position, and squeeze out the excess mortar, and finally compact and press the brick joints through the grooves.

(2) Expansion joints and sliding layers. The masonry will expand greatly from cold to hot. The carbonization chamber expands toward the external space in the longitudinal direction, and the longitudinal expansion of the furnace body mainly relies on the expansion gap to keep the center distance of the combustion chamber basically unchanged during production. For this reason, the width of the expansion joint should be adapted to the expansion amount of the masonry after heating. The working temperature of each area is different from all refractory materials, so the expansion amount is also different, and the number and width of the expansion joints left in each place are also different. Usually, the expansion of the silica brick coke oven ramp area can be calculated as 2%, that is, the expansion joint per meter (including mortar joint) is calculated as 20mm. If the expansion joint is too small, the masonry will be squeezed, deformed or cracked; if it is too large, there will be gaps left after expansion, which is easy to cause leakage. The quality of the expansion joint is mainly guaranteed by the width of the joint and the flatness of the joint wall. Therefore, it is necessary to use the expansion joint template for masonry, and the thickness of the board is 1~2mm less than the width of the expansion joint. In order to keep the joint wall flat, the brick surface close to the expansion joint must be flat during processing, usually by mechanical processing. The expansion joint should be filled with fillers according to the width of the joint. When the gap is narrow, horse manure paper is placed during bricklaying. When the gap is wide, the expansion joint template is used to build and clean it, and then sawdust is filled in, and asphalt is poured on it. The sawdust should be dry, clean, and free of other impurities. The softening point of asphalt should be appropriate, generally 65~80℃.

Using the expansion joint to absorb the expansion of the furnace body is achieved by the relative displacement of the masonry on both sides. Therefore, a sliding layer must be set above and below the expansion joint, usually asphalt felt paper, kraft paper or horse manure paper (the former is better) is dry-laid in the expansion joint to allow the furnace body to move relatively. The length of the paper used for laying the sliding layer is such that one end covers the lower expansion joint by about 5~10mm to prevent the mortar from being squeezed into the expansion joint when the upper bricks are laid, which will affect the sliding of the masonry. The other end extends to the edge of the upper expansion joint to prevent the paper from being hooked out when cleaning the upper expansion joint, which will affect the quality of the sliding layer.

(3) Straightness, verticality and elevation error of the masonry: Since various coke oven equipment must be installed after the furnace body is built, and it must be operated in coordination with various related mechanical equipment during the production process, there are strict requirements for the elevation dimensions of the furnace body and the flatness of each wall.

The elevation error of the masonry refers to the difference between the elevation of the actual brick layer and the design elevation of the brick layer. The elevation error can be used to measure whether the masonry accurately meets the design requirements and its coordination with the coke oven equipment. The elevation of the masonry should be measured regularly with a level meter, and regular inspection can be compared with a level ruler or a wooden ruler and a vertical benchmark.

The straightness of masonry refers to the degree of unevenness on the surface of a certain area of masonry. It is generally measured with a 2mm long wooden ruler along any direction of the masonry surface.

The verticality of masonry refers to the degree of deviation of the vertical line on the vertical surface of the masonry. It is generally measured by the plumb bob method.

Although verticality and straightness are closely related in some cases, that is, the straightness of the vertical surface of the masonry is included in the verticality of this surface. When the flatness is not good, the verticality is not good either, but the errors of verticality and straightness are not necessarily consistent.

The verticality and straightness of the wall are one of the main indicators for measuring the quality of masonry. In particular, the wall of the carbonization chamber should be strictly controlled. Excessive errors in verticality and straightness will cause difficulties in pushing coke and lead to early damage to the furnace wall.

(4) The dimensions of the channels of each part of the coke oven and the channels between them. The cross-section and relative position dimensions of the channels of each part of the coke oven masonry are also one of the main indicators for measuring the quality of brickwork. Some will affect the smooth installation of equipment after the furnace is built, while others are very important for ensuring the temperature adjustment and normal heating of the production process. Therefore, in addition to paying attention to bricklaying, the size of refractory bricks should also be strictly checked and selected.

2 Main precautions for bricklaying in various parts of coke ovens

According to the requirements of the coke oven structure, the bricklaying of coke ovens includes five structural units: small flue, heat storage chamber, inclined area, carbonization chamber and furnace roof. The common requirements for these five units are: the mortar joints are full and uniform, the wall surface is horizontal and vertical, and the geometric dimensions of the coke oven meet the tolerance requirements. In addition to these general requirements, there are also their own precautions.

(1) Small flue, the small flue is the beginning of the coke oven masonry. It is built on the top plate of the coke oven foundation. The thermal expansion of the two is different. Therefore, there is a sliding layer between the top plate surface and the red brick layer above it. Generally, clean river sand can be used. The thickness of the sand layer is required to be uniform and meet the design requirements. Try to lay it as you lay it. The key is to ensure sliding. After the first layer of bricks in the small flue is laid, it is necessary to prevent sliding displacement and deviating from the design size, causing problems such as the furnace head moving outward, the hole width changing, the wall width increasing and the vertical joints not being full. The first furnace head should be built in 4 to 5 layers and in a stepped manner towards the middle. The first layer of furnace head is the starting point of bricklaying for the entire furnace, which has a great impact on the quality of subsequent masonry. Therefore, it should be built strictly according to the center point and front line of the standard plate.

When laying the grating bricks, be careful not to mix the numbers, otherwise it will affect the reasonable distribution of the subsequent heating airflow. The expansion joint width of the grating bricks must be guaranteed, and the bricks should be processed if it is insufficient. The grating brick footrest is the basis for placing the grating bricks, and its straightness should meet the quality requirements of no more than ±5mm.

The two sides of the central partition wall of the two-part coke oven are in opposite directions of airflow, so tightness is particularly important.

(2) Regenerator, during the masonry process, pay attention to controlling the center line of the wall to prevent the width of the regenerator hole from being too small and affecting the placement of the grating bricks. For this purpose, the hole width can be built into a negative tolerance.

To ensure that the ramp area is built smoothly, the elevation of the top of the heat storage chamber and the adjacent walls should be checked. It is generally stipulated that the elevation of the adjacent wall of the top of the heat storage chamber should not exceed 3mm, and the error between the top of the heat storage chamber and the design size should not exceed ±5mm.

The position and center distance of the gas pipe bricks should also be strictly controlled in the bottom-spraying coke oven to ensure that the pipe bricks are vertical and meet the design size. The joints between the pipe bricks should be full of mortar to avoid leakage and explosion during production. The excess mortar in the pipe bricks should be cleaned as they are laid.

(3) The ramp area is the most complex area in the coke oven structure and brick type. There are many channels, and heating gas, air and exhaust gas all flow through it. If the brick joints are not tight, it is very easy to cause leakage, affecting the normal production of the coke oven. Therefore, the brick joints in the ramp area should be built tightly, and the use of brick insertion method should be minimized or avoided. Since the brick joints in the ramp area are mostly hidden joints, the joints should be grouted immediately after each layer of bricks is laid.

To ensure smooth coke pushing, the bottom bricks of the carbonization chamber shall not be misaligned in the opposite direction of the coke cake pushing out, and the surface shall not have defects. To ensure the position and size of the ramp opening, the opening size of the ramp opening bricks and the gas duct pipe bricks should be selected and checked piece by piece. Before laying the first layer of bricks in the ramp, the carpenter should mark the center line of each opening. The ramp outlet at the top layer of the ramp area is in the direction where the adjustment brick cannot be adjusted, and the allowable error is ±1mm. The requirements for brick gas ducts in side-entry coke ovens are the same as those in bottom-spraying coke ovens.

(4) Carbonization chamber, the carbonization chamber of the coke oven is alternately arranged with the combustion chamber, and the bricklaying of the carbonization chamber is also the bricklaying of the combustion chamber. Before laying bricks in the carbonization chamber, the bricklaying quality inspection of the ramp area should be completed, and all channels and holes should be thoroughly cleaned; the lamp head mouth of the brick gas duct outlet should be plugged with paper and filled with asphalt. To ensure the correct position of the first layer of bricks in the carbonization chamber, the carpenter should mark the top surface of the ramp area with ink lines for positioning and then lay bricks. In order to prevent the mud from clogging the ramp and the bottom of the vertical fireway, and to prevent bricks from falling and damaging the ramp opening, after 2-3 layers of carbonization chamber wall are built, clean the ramp opening and the bottom of the vertical fireway again, sprinkle 10-15mm thick sawdust on the bottom of the vertical fireway, and then put a special temporary protective plate. The carbonization chamber and the combustion chamber are separated by only a thin wall. If there is a gap, the raw gas will leak into the combustion chamber and burn, destroying the normal heating of the coke oven. And reduce the quality of coke. For this reason, all brick joints should be full and tight, and the joints should be thoroughly pointed every 4-5 layers.

The width of the carbonization chamber should meet the design size, and there must be no contrast between the machine and coke sides. The wall surface should be smooth and there should be no misalignment in the opposite direction of the coke pushing direction, just like the bottom surface of the furnace.

The shoulders at both ends of the combustion chamber are where the protective plates and furnace door frames are installed. The front line should not differ from the design requirements by more than ±3mm, and the shoulder flatness and verticality errors should not exceed 3mm. Otherwise, when installing the protective plates and furnace door frames, the asbestos ropes on the shoulders will be loose or tight, which may cause air leakage after production and cause smoke and fire. When laying the furnace end wall, attention should be paid to the size and cleaning of the expansion joints.

(5) Furnace top. The characteristics of the furnace top part are that there are many units, different structures, and chaotic construction. Therefore, before construction, the center line and edge line of the coal loading hole and the riser hole should be accurately drawn, and then the carbonization chamber cover bricks should be laid according to the edge line. When laying the cover bricks, the expansion joints should be uniform, and the length of the carbonization chamber should not exceed the shoulders to avoid affecting the installation of the furnace door frame.

When laying the fire hole wall, attention should be paid to the center distance of the fire hole, the brick layer elevation and verticality, and the inner wall misalignment should not exceed 2mm. It is also necessary to prevent bricks and mud debris from falling into the vertical fire channel, and the internal brick joints should be hooked as they are laid. The last layer should be built with the pre-prepared fire-watching hole and coal-loading hole base, and the fire-watching hole cover and coal-loading hole cover should be oiled and covered immediately. The masonry of the coal-loading car track foundation should be carried out according to the pre-marked lines and should not be skewed.

3. Finishing work

After the entire coke oven is built, it is necessary to thoroughly check all parts of the furnace body and remove any debris and tools left in the bricklaying process. The brick joints on the surface of the masonry, including the wall of the carbonization chamber, are grouted twice. All expansion joints exposed to the outside should also be cleaned and blocked with asbestos ropes. The front of the furnace head of the combustion chamber of the coke oven using a small protective plate needs to be applied with a 10mm thick plastering layer to ensure good contact between the furnace body and the protective plate, and the furnace body is evenly stressed. It is required to be straight and vertical, and the deviation from the front line should not exceed ±3mm.

After cleaning and inspection, the heat storage chamber needs to be placed with checkerboard bricks (the checkerboard bricks should be placed as the lower adjustment coke oven is built). Checkerboard bricks are dry-laid. In order to keep it stable and vertical, horse manure paper can be used to level it. When placing, the first layer of bricks should be laid first according to the design requirements, and then laid outward in a step-like manner from the inside to the outside. Attention should be paid to aligning the holes of the upper and lower layers, leaving enough expansion joints, and finally building the sealing wall. Other work includes burying iron parts, laying the lining bricks of the furnace door and riser, laying the ox tongue bricks, etc. The finishing work must also be done well, otherwise it will affect the quality of the coke oven.