Most exergy uses purified natural gas to replace m

2022-08-08
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Replace methanol with purified natural gas Abstract: Anhui Xingrui gear transmission Co., Ltd. has successfully replaced methanol acetone with purified natural gas for gear carburization. The results of this project show that the product quality is steadily improved, the production cost is significantly reduced, and the purified urban natural gas has a broad prospect of being used within ± 0.1% of the set value in the heat treatment industry

key words: purified natural gas, heat treatment, economic benefits

1, preface

in the traditional concept, the carburizing medium is generally methanol acetone, kerosene, methanol propane, etc. these media have a common weakness is the need to build a repository, which lays a major hidden danger for safe production. As a wide range of energy, natural gas has the advantages of low price and safety, It has been carburized by more and more manufacturers as heat treatment medium

2. Reaction principle

the formula for preparing endothermic atmosphere with natural gas is: ch4+2.38 air -->co+2h2+1.88n2, Ni is the catalyst, and the reaction temperature is ≥ 1000 ℃. According to the above formula, the ratio of natural gas to air is 1:2.38, while the actual situation is generally 1:2.5, or even higher, because natural gas not only contains methane, There are also compounds with high carbon content such as propane and harmful impurities

rx atmosphere preparation reference table:

natural gas (CH4) + air preparation RX atmosphere

gas production temperature 1000 ~ 1040 ℃, natural gas: air =1:2.4, dew point -2 ~ 5 ℃

the ratio currently used by our company is 1:2.8, which is the highest number we know: dew point -2 ~ 5 ℃. Generally, the air ratio is adjusted appropriately during work, because this can ensure the complete cracking of natural gas and is not easy to accumulate carbon black, At the same time, the feed gas and natural gas for RX atmosphere preparation are saved... About 15%. Due to the very good purification of natural gas, the consumption is greatly reduced when the rich gas is 2m3/h, which makes the carburization mechanism of CH4 → cad+h2 play a full role. It not only does not produce carbon black, but also reduces the carburizing mechanism with the participation of oxygen, and the non martensitic structure produced by internal oxidation on the surface layer of carburized parts is greatly reduced (shallow corrosion), as shown in Figure 3

the schematic diagram of natural gas carburization and quenching is as follows:

the principle of using methanol acetone carburization is:

3. The advantages of using natural gas for heat treatment

take methanol acetone as an example to compare the advantages of natural gas

3.1. Convenient transportation, purchase and transportation

methanol and acetone are liquids, which are inconvenient to transport and costly, while natural gas is transported by urban pipelines, which is very convenient. Acetone is one of the raw materials for manufacturing drugs. It is a strictly controlled chemical product, which is difficult to buy, and natural gas is used by every household. Methanol and acetone must be pumped to a certain height or transported with gas of a certain pressure before being transported into the equipment, while natural gas can be directly transported into the equipment only after proper decompression

3.2. Simple management

when using methanol and acetone, a well ventilated medium room must be built, and the construction of the medium room will have potential safety hazards and bring trouble to the safety work; Using natural gas avoids the trouble of building a medium room, and the construction cost is low. Even if there is a fire on the ground, the pipeline solenoid valve will automatically cut off, and there will be no fire

3.3. Product quality improvement

methanol and acetone are liquid media. After dripping into the equipment, there is a process of gasification → decomposition. There are a lot of water, organic sulfur and inorganic sulfur in the methanol, which makes the medium pipe easy to accumulate carbon black. According to reliable information: some factories have ordered methanol purification equipment to improve the quality stably, thus making the workpiece surface not bright and clean; Natural gas is a gaseous medium. After entering the equipment, it does not need gasification process, and is directly decomposed into activated carbon and hydrogen without oxygen, which is not easy to form carbon, and the surface of the workpiece is clean; The non martensitic structure of the surface layer of carburized parts is greatly reduced. Generally, when the effective hardening depth is 0.8 ~ 1.2, the tooth pitch position is 5 μ M (shallow corrosion), and the surface layer hardness (HV1 conversion) is above HRC61. See figure

3.4. Production cost reduction

the following table is the natural gas consumption record of aixielin single push continuous furnace after it is normally put into production:

if the market price of natural gas is calculated at 3.0 yuan/m3, the medium use cost of aixielin continuous furnace is 3.0 yuan/m3 × 2.5m3/h=7.5 yuan/h

next, let's roughly estimate the medium use cost of Ipsen furnace in the old area

methanol 4000kg/month × 4.2 yuan/kg=16800 yuan/month, acetone 1600kg/month × 14.6 yuan/kg=23360 yuan/month, liquefied gas 800kg/month × 5.5 yuan/kg=4400 yuan/month, then the use cost of Ipsen continuous furnace medium is (16800 yuan/month +23360 yuan/month +4400 yuan/month) ÷ 30 days ÷ 24h=61.89 yuan/h

from the above comparative data, it can be clearly seen that using natural gas as carburizing medium for heat treatment saves costs compared with methanol and acetone

saving estimation: (61.89 yuan/hour -7.5 yuan/hour) × 24h × 30 days × December =469900 yuan/year, and the investment of the equipment used will be recovered within 9 months

3.5. Less carbon black accumulation

from the actual use situation, at present, the aixielin continuous furnace has been put into use for about half a year. Since the spare methanol acetone pipeline was removed, there has been no carbon black accumulation. When observing the furnace from the peephole, there is no obvious carbon black, and there is no carbon black attached to the workpiece out of the furnace. Appear bright silver gray without carbon black. Quenching oil is also pollution-free and clear

4. Key points to pay attention to in the process of use

4.1. Purified natural gas

urban civil natural gas

the prerequisite for carburization of natural gas is that its purity must be greater than 95%, and the sulfur content must be less than 10mg/m3 (the lower the sulfur and water content is, the better) [1.2], because sulfur and water corrode pipelines and equipment seriously, which greatly increases the consumption of heat treatment gas source and reduces the quality of products. Therefore, natural gas needs to be purified. Our company also knows that many units have a service life of more than 10 years due to the purified index and the maintenance of the index in the bidding work; In the market, all kinds of desulfurization, purified natural gas and other manufacturing units have stopped, and dare not accept the bid. Finally, the mature Chinese invention patent "natural gas purification equipment" which has been widely used in enterprises in Germany, the United States, Japan and South Korea in China will be used to purify urban natural gas

the equipment features low investment: compared with the two-step desulfurization of organic and inorganic sulfur in natural gas, the initial desulfurization effect of this method is lower than that of the invention patent, and the effect of the two-step desulfurization is getting lower and lower after half a year (sulfur only eats, does not spit, but also produces water, and intestinal obstruction). In the two-step desulfurization, the removal of inorganic sulfur by mixed solid method such as fe2o3zno2 or wet alkali method brings a lot of moisture, which is very unfavorable to the carburizing atmosphere of heat treatment. The old activated carbon removal of organic sulfur in natural gas generally fails after 50 regenerations. The investment of this equipment is reduced by more than 1/2, and the land occupation is reduced by more than 2/3. After being put into operation, the operation cost is low, and the purification effect is good

comparison of effects before and after natural gas purification

note: intestinal obstruction will not occur when the external pressure is very low; When the inorganic sulfur of external natural gas mine desulfurization equipment is up to 1100mg/m3 during maintenance, it is OK to shorten the regeneration cycle and will not stop production. (due to the great fluctuation of sulfur in the external gas source, it has been verified by six users of West to east gas transmission project. Generally, the regeneration spits dirt for 10 hours, and some customers spit dirt gas after regeneration for 72 hours

※ this data is detected by a trace moisture detector. If the dew point meter is used ≤ -60 ℃.

the service life of the purifier is long (service capacity): Chongqing machine tool plant has been used for 19 years, and it can still meet the service capacity of the above indicators at present. The plant uses purified gas source heat treatment equipment, so far only minor repair, not overhaul, saving considerable value

the natural gas purified by our company has no rotten egg smell, and the flame is blue. After testing, the total sulfur is less than 1mg/m3, which proves that the purification effect is stable and very good

the purification agent used in the purification tank carries out chemical reaction, electrochemical reaction, physical adsorption and physical filtration on the impurities in natural gas, such as organic sulfur, inorganic sulfur, water, oil and mercury. When the absorption is saturated, regeneration is required. Our company uses compressed air to regenerate the purification tank. Because regeneration requires heating (about 350 ℃), In this way, some stubborn sulfides, especially Tetrahydrothiophene in organic sulfur, can be completely separated out, and water, oil, and mercury can be separated out at the same time, but this brings a problem. While sulfide is separated out, the water adsorbed by the purifier is heated and converted into water vapor, which is condensed into water through a long pipe, and then accumulated and ejected from the pipe combustion port, thereby watering the ignition nozzle of the gas generator and the exhaust gas emission flame, Cause the gas generator to stop working

after detailed analysis and Research on the problem, we have discussed and come to a simple and effective scheme - simple reconstruction of the pipeline can easily solve the above problems. The attached diagram is as follows

it is obvious from the above figure that the problem of water spray can be solved by simply modifying the original pipeline, changing the elbow into a tee of corresponding size, connecting a pipe with gradient of appropriate length, and installing a ball valve at the end of the pipe. When the water vapor condenses into water, it will accumulate in the modified storage pipe. Open the ball valve every few hours to drain the water (the actual experience is to drain the water every 3 hours). It is suggested to add a water gas separator on the regeneration pipeline. (the R & D and manufacturing unit has increased the installation of a water gas separator)

4.2. Process adjustment

for general through continuous furnaces, the exhaust gas emission in front of the furnace is greater than that behind the furnace, with a proportion of about 7:3, so as to ensure equipment safety and product quality. In this way, the medium flow in each zone should be gradually reduced from front to back. On the premise of abiding by this big code, aixielin continuous furnaces, after repeated adjustment, slightly increase the medium flow in the insulation zone, so as to ensure the carbon potential of the insulation zone, At the same time, the natural gas has also been fully decomposed (the carbon determination results are basically consistent with the instrument display)

4.3. Pressure reducing valve

in the process of using natural gas, one thing to pay attention to is the pressure to be used. First, it is necessary to connect with the carburizing furnace manufacturer in detail to understand the flow and pressure required by the equipment, then combined with the future plan of the plant, and finally consider the appropriate margin. Many comprehensive factors are combined to form the final requirements for the pressure and flow of natural gas required by the natural gas company. Since the medium pressure (0.02 ~ 0.07MPa) is used for urban natural gas, and the pressure used on the carburizing furnace is only 3 ~ 5kpa, it is necessary to reduce the pressure appropriately. When selecting the pressure reducing valve, be sure to tell the manufacturer the pressure before and after pressure reduction, so as to ensure the selection of a suitable pressure reducing valve

4.4 leak detection

as natural gas is a flammable and explosive gas, although it avoids the trouble of building a media room, it cannot be taken lightly in the process of use. The leakage of pipelines should be detected regularly, usually once a month, and the joints such as loose joints, elbows, ball valves and so on should be mainly inspected. There are many inspection methods, and soapy water can be used with enterprises as the main body and market as the guide, Portable CH4 gas leak detector of similar size produced by professional manufacturers can also be used. The pressure gauge and corresponding supporting facilities should be checked frequently, and air leakage should be handled in time

4.5. Sudden gas shutdown

what should be done when natural gas is used for carburization and exhaust gas ignition? This issue has been repeatedly communicated with natural gas companies

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