[Abstract] A hundred years ago, in the field of metal welding and cutting, the earliest used is hydrogen. However, due to its poor performance, it was gradually replaced by acetylene. At present, due to the serious pollution problem of acetylene in calcium carbide method, it is necessary to find alternatives, and hydrogen and oxygen cutting has been discovered and studied again. However, according to the HBC-13 standard promulgated by the State Environmental Protection Administration, because the temperature of the oxyhydrogen flame is lower than 3000 °C, it is still unqualified metal welding and cutting gas. This paper includes: (1) according to the principle of the same workload, the appropriate analysis of the economic benefits of hydrogen and oxygen cutting; (2) proposed improvements, that is, the formation of hydrogen: "NAS" gas = 1:1 Mixed gas, the flame temperature is greater than 3100 ° C, the density of 1.07 ~ 1.12 is less than air, the explosion limit of 2.6 ~ 17.1% (body). It will be possible to add another option when replacing acetylene in a shipyard without natural gas! Item Mixed gas Composition (% by volume) Hydrogen 50+ "NAS" gas 50 references East China University of Science and Technology Huang Guoxiong Window Screen,Window Net Screen,Window Screen Roll,Metal Window Screen ANPING HONGYU WIREMESH CO.,LTD , https://www.hongyu-wiremesh.com
Foreword
At the beginning of the last century, in the early stage of steel oxygen flame cutting, hydrogen was the main preheating gas, but due to the small volumetric heat of hydrogen, the flame temperature was low (2100~2600 °C), the warm-up time was long, and the safety was poor ( The shortcomings of the explosion limit in air (4.1%~74.2%), and later gradually replaced the other gases such as acetylene with high flame temperature (3100~3300 °C) [1], [2].
In the 1980s, due to the serious environmental pollution problem of acetylene in calcium carbide process, the raw material of hydrogen-oxygen mixed gas is water, and the combustion product is also water, which has no pollution to the environment. Therefore, in the United States, Switzerland, and the former Soviet Union and other countries, small-scale electrolyzed water hydrogen and oxygen generating devices have been developed, and the hydrogen-oxygen mixed gas produced by the same has been used as the metal welding and cutting gas. It is called "hydrolyzed hydrogen-oxygen flame gas cutting method".
There has been constant research in our country. The JF series have been successfully developed; CCHJ series; TGHJ series; DQS series; YJ series of MCC Group.
"Hydrogen and oxygen cutting" as a kind of acetylene substitute gas, its performance characteristics are as follows:
(1) No pollution: The production process is rarely polluted, the combustion products are water, non-toxic, odorless and smokeless.
(2) Poor safety: The explosion limit is equivalent to acetylene (the explosion limit in oxygen is 4.7~93.9%), while the combustion rate of hydrogen and oxygen is higher than that of acetylene, and the explosion risk is greater. Two tempering preventers and rupture disks must be provided.
(3) Low flame temperature: narrow range of use, in the shipyard fire workshop where high temperature flame is required, spray remelting, large thickness cast steel, steel ingot cutting (450mm or more) can not replace acetylene. According to the technical requirements of “Metal welding and cutting gas†promulgated by the State Environmental Protection Administration in October 2002, Article 4.3 of HBC-13-2002 “The flame temperature of the product when burning in oxygen must be above 3000 °C.†Simple hydrogen-oxygen mixing Gas (2100~2600oC) is a non-conforming product.
(4) Energy-saving: Basic electrolysis of hydrogen and oxygen requires electricity and water. In terms of energy saving, it is not necessary to consume natural gas, propane, and the like. Even if it is hydrogen, different sources, the hydrogen is more energy-consuming and more expensive than the hydrogen obtained from the nitrogen-hydrogen mixture of the fertilizer plant by pressure swing adsorption or Monsanto membrane separation.
Compared with the acetylene method of calcium carbide method, MCC Group stated that “the hydrogen consumption per kilometer of hydrogen produced by steam is 4.0 degrees, and the production of 1m3 acetylene consumes 15.84 degrees. The replacement of acetylene with hydrogen and oxygen can save a lot of energyâ€, but the total heat of 1m3 acetylene The value is 55.2 MJ. The 1m3 hydrogen oxygen is only 8MJ. Whether this can be compared is controversial.
(5) Economic benefits: In terms of economic benefits, the same, China Metallurgical Co., Ltd. believes that the cost of hydrogen and oxygen cutting gas is only 30% of acetylene and 40~50% of propane, propylene and other gas when flame cutting continuous casting billet. It also needs further verification!
This article will specifically analyze the economic benefits of hydrogen and oxygen cutting. And put forward some ideas for the development of hydrogen-oxygen cutting!
First, how to correctly evaluate the economic benefits of different gas
Different kinds of gas properties are different. Therefore, regardless of the equal volume; according to the same weight; according to the equal heating value; or a bottle of gas consumption of a few bottles of oxygen, etc., there are certain defects.
Whether it is acetylene or substitute gas, it is used to cut steel, so the total cost of gas or gas and oxygen consumption is calculated according to the same workload. Which kind of gas is saved is the real economic benefit! [3], [4], [5]
Second, the test data
(1) Shandong Qingdao Steel Plant used hydrogen-oxygen cutting for hot cutting of continuous casting machine rail steel. Each torch requires two oxyhydrogen machines. Each oxyhydrogen machine nameplate has a power of 25KW and a hydrogen production capacity of 6.3m3. /Time. The price of each YJ series of oxyhydrogen machines is 49,500 yuan. The cut billet is 140 mm x 140 mm square steel. This shows:
(1) Each torch uses hydrogen gas per hour of 6.3 x 2 = 12.6 m3. The electricity consumption per 1m3 of hydrogen and oxygen is 4 degrees, and the local industrial electricity cost in Qingdao is 0.715~0.79 yuan/degree. Now calculated at 0.715 yuan / kWh. 1m3 hydrogen oxygen electricity cost, 4 degrees × 0.715 yuan / degree = 2.86 yuan / m3, the gas cost per torch per hour is: 12.6 m3 × 2.86 yuan / m3 = 36.04 yuan / hour
(2) The value of the two oxyhydrogen machines is 49,500 × 2,100,000 yuan, which requires depreciation and overhaul costs, plus five liters of water consumption per hour, which is calculated as 2 yuan per hour.
(3) The total cost of a continuous casting machine torch with hydrogen oxygen is 36.04 + 2 = 38.04 yuan / hour
(2) Jiangyin Xingcheng Steel Plant (3# continuous casting machine of Sanlian Branch)
1. Billet specification: 140×140 = 2800mm (weight 400kg);
2, steel type: 20MnSi;
3, cutting speed: 1.8m / min (number of cutting per hour = 1.8 × 60 / 2.8 ≈ 38 knives).
When using propane (Shengpu gas, 5900 yuan per ton), 0.32 kg of propane per ton of steel is cut, and 2.5 knives per ton of steel is cut.
The propane was 0.32 / 2.5 = 0.128 kg / knives per knife, and the propane consumption per hour was 0.128 × 38 = 4.86 kg / hr. The propane cost per hour was 4.86 × 5.9 = 28.7 yuan / hr.
When using "NAS" gas (1 million tons per ton of "NAS" gas), cutting 0.124kg per ton of steel, then use "NAS" gas for each knife.
0.124/2.5=0.05kg, “NAS†gas consumption per hour is 0.05 kg/knife×38 knives/hour=1.88 kg/hr, hourly “NAS†gas cost is 1.88 kg/hr×12 yuan/kg=22.6 yuan /Time.
(3) A brief comparison with acetylene
In the case of general "NAS" gas and acetylene cutting, the same workload is "NAS" gas: acetylene = 1: 1.2 [3] (weight ratio).
The average price of acetylene is between 1.5 and 18,000 yuan/ton, with an average of 16,500 yuan/ton. If acetylene is used: the amount of acetylene per hour is: 1.88 × 1.2 = 2.6 kg / hour, the acetylene cost per hour is: 2.26 kg / hour × 16.5 yuan / kg = 37.3 yuan / hour. If the amount of acetylene per hour is converted to a volume of 2.26 / hour / 1.17 kg = 1.93 m3 / hour. In the test data (1), hydrogen oxygen was used at 12.6 m3 per hour.
According to the data of MCC: 1m3 acetylene consumes 15.84 degrees, then 1.93 m3/hour consumes 30.6 degrees/hour; 1m3 hydrogen oxygen consumes 4.0 degrees, then 12.6 m3/hour consumes 50.4 degrees/hour.
It can be seen that hydrogen and oxygen cutting is the most expensive when the workload is the same. The same 1m3 acetylene workload is required to complete 1.26 / 1.93 = 6.53 times hydrogen and oxygen.
Gas name Hydrogen oxygen Acetylene Propane "NAS" gas Price per ton of gas (ten thousand yuan) 3.2 1.65 0.59 1.2
Price per kg of gas (yuan) 32 16.5 5.9 12
The price of 3 gas per meter (yuan) 2.86 / / /
Single torch:
Air consumption per hour 12.6m3 2.26kg 4.86kg 1.88kg
Fuel cost per hour (yuan) 38.04* 37.3 28.7 22.6
Equivalent power consumption per hour (degrees) 50.4 30.6 / /
*Additional depreciation, etc. about 2 yuan / hour
Gas density, 0oC, 0.1Mpa (kg/m3) 1.07~1.12
Flame temperature (oC) ≥ 3100
Maximum burning speed (oC) 7.5~11.0
Fire point, air (oC) 459~494
Explosion range (in air, volume %) 2.6~17.1
Theoretical oxygen consumption ratio 3.0
Third, the results are compared:
It can be seen that: (1) According to the principle of the same workload, after comparing hydrogen, oxygen, acetylene, propane and “NAS†gas, it is found that hydrogen and oxygen have the worst economic benefit. Of course, the electricity bills vary from place to place, resulting in a large change in the cost of hydrogen-oxygen cutting. It is best to multiply the local electricity bill by 50.4 degrees per hour for comparison! (2) In view of the cost of electricity, hydrogen and oxygen cutting consumes the most electricity. At present, the domestic power gap is large, and caution should be taken when using hydrogen and oxygen cutting.
Fourth, the idea of ​​improving the hydrogen and oxygen cutting process
The fatal shortcomings of hydrogen-oxygen cutting are: (1) low flame temperature; (2) wide explosion limit and poor safety.
According to the author's investigation [1], if the hydrogen-oxygen generator is transformed into a hydrogen and oxygen shunt. Pure hydrogen is blended with the "NAS" Nass gas invented by the author to become a mixed gas. At this time, the physical and chemical properties of the mixed gas are as follows:
According to the performance in the table, the mixed gas has good safety, high flame temperature and low density than air, and is suitable for use in shipyards and ship cabins. The economic benefit is better than pure hydrogen oxygen cutting. In places where there is no natural gas source, the shipyard has completely replaced acetylene, and there is another option!
1. Editor-in-Chief Liang Guifang, Cutting Technical Manual, Mechanical Industry Press, 1999
2, Li Yajiang, etc., cutting technology and application, Chemical Industry Press, 2004
3. Huang Guoxiong et al. Study on the quality evaluation index of acetylene substitute gas, factory power, 1999(4)32~37
4, Huang Guoxiong, etc., research on acetylene substitute gas quality evaluation index (2), factory power, 2003 (2) 25 ~ 29
5. Huang Guoxiong et al. Economic Benefit Analysis of Propane and Propylene Substituting Acetylene, Proceedings of Shanghai Welding Society Annual Conference, 2004
Author
Shanghai Xiongcheng Industry and Trade Co., Ltd. Huang Xinqun