Production of sodium formate from calcium carbide furnace exhaust gases
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1 The Chinese calcium carbide industry faces both opportunities and risks. Due to the continuous rise in international crude oil prices, domestic manufacturers that produce PVC using the ethylene method are facing losses. Currently, 85% of the world’s PVC production capacity relies on the ethylene process. Oil prices are expected to remain high in the coming years, and these high costs will prevent a sharp drop in the prices of PVC produced via the ethylene process ； Technological advancements are enabling the performance of PVC produced by the calcium carbide method to gradually approach that of PVC produced via the ethylene method, so the price difference between the two will not widen significantly. At the same time, calcium carbide-based PVC has a significant cost advantage over ethylene-based PVC. Therefore, the calcium carbide method for PVC will experience a long-term \"bull market\" in China. As China’s calcium carbide industry enters a golden age, it still faces severe policy and environmental risks. In October this year, the **National Development and Reform Commission officially issued the \"Access Requirements for the Calcium Carbide Industry (Revised in 2007)\"). The newly revised requirements set stricter rules regarding the scale of new capacity to be established, the phasing out of outdated production capacities, technical equipment, energy consumption, and the comprehensive utilization of resources. A large number of outdated and scattered calcium carbide plants in the central and western regions of the country will be forced to close. According to the third membership conference of the National Calcium Carbide Association held this year, China’s calcium carbide industry has entered a period of rapid development. As of September 2007, the national production of calcium carbide was 10.72 million tons, with an expectation that it would exceed 14 million tons for the whole year, representing a growth of over 20% compared to 2006. Over the past five years, the capacity and production of calcium carbide have been growing at a rate of 27%. The total pollution generated by calcium carbide furnaces is enormous. To produce 1 ton of calcium carbide, a calcium carbide furnace consumes 205.7 cubic meters of O2 and emits 565.7 cubic meters of CO2 gas. So in 2007, 14 million tons of calcium carbide were produced, resulting in a total emission of 7.92 billion cubic meters of CO2 gas. If the CO2 emitted from semi-coke and lime burning is added in, the total CO2 emissions to sustain the calcium carbide industry are astonishing. There is significant thermal energy loss in the off-gases from calcium carbide furnaces. To produce 1 ton of calcium carbide in a closed calcium carbide furnace, 400 cubic meters of CO gas at 90% concentration are emitted, which is equivalent to burning 200 kilograms of standard coal needlessly. Based on a calcium carbide production of 14 million tons in 2007, this equates to 2.8 million tons of standard coal. At present, some areas use the exhaust gases from calcium carbide furnaces to generate electricity, produce lime, or operate waste heat boilers; however, this is merely a temporary solution that does not address greenhouse gas emissions at their root. Moreover, the added value of burning these exhaust gases is low. Only by converting these exhaust gases into chemical products can greenhouse gas emissions be truly addressed, the added value of these gases increased, and the circular economy structure of the calcium carbide industry improved. 2 Study on the properties of calcium carbide furnace exhaust gases and purification processes 2.1 Characteristics of calcium carbide furnace exhaust gases in different furnace types Calcium carbide furnaces can be classified into three types based on their design: open-type furnaces, semi-enclosed calcium carbide furnaces, and fully enclosed furnaces. Different furnace types result in completely different flue gas properties. Open-type calcium carbide furnaces produce large amounts of flue gas with a low temperature, generally not exceeding 200°C℃ ； The flue gas temperature in semi-hermetical calcium carbide furnaces is relatively high, generally exceeding 400°C, resulting in a significant reduction in the amount of flue gas ； The fully enclosed calcium carbide furnace has the highest flue gas temperature, ranging from 400 to 1000°C, but the volume of flue gas is very low – 90% less than that in semi-enclosed calcium carbide furnaces – resulting in less pollution. In addition to the furnace type, different regions, process flows, operating methods, and raw materials all affect the flue gas characteristics of calcium carbide furnaces. The basic requirements for calcium carbide furnaces to implement the technology of this project are: sealed calcium carbide furnaces with a capacity of 12,500 kVA or more. 2.2 Study on the physical properties of exhaust gases from closed calcium carbide furnaces. The temperature at the top of these furnaces ranges from 400 to 1000°C. 400 Nm3 of furnace gas is generated per ton of calcium carbide produced. The composition of the carbide furnace gas is shown in Table 1. Table I Composition of the gas from calcium carbide furnaces. Sequence Number, Name, Percentage Content (%), Content (g/m3), Remarks: 1, Carbon monoxide >70–90, 2, Hydrogen
Are there any mature industrialized devices available?
The production cost of sodium formate from calcium carbide furnace exhaust gas is 2,600 yuan per ton. In August 2008, the market price of sodium formate in Shanghai was 3,000 yuan per ton. Most manufacturers of calcium carbide furnaces are located in the western region, resulting in long transportation distances to the target markets; if road transport is used, the logistics costs are high. If these logistics costs exceed 400 yuan per ton (with normal logistics expenses ranging from 400 to 600 yuan per ton), it becomes unprofitable to produce sodium formate； Only by utilizing the low-cost transportation mode of railways can the meager profits of sodium formate products be maintained.
Given the current conditions in domestic and international markets, the calcium carbide process for PVC has almost no advantages. Of course, only if oil prices rise in the future can the advantages of this process be considered, as well as the potential use of calcium carbide furnace gas. Regardless of the application area for calcium carbide furnace gas, it at least indicates that the products manufactured using it have market viability; otherwise, the investment would not yield a worthwhile return. Whether used for power generation, lime burning, or boiler preheating, it reduces the amount of fuel required by the same extent; therefore, it’s impossible to determine how many tons of standard coal are saved. Of course, the sales of sodium formate also need to be taken into consideration; if this issue is not resolved properly, it will ultimately lead to the shutdown of the plant.
After applying our company’s project technology to the exhaust gases from the two 25,500 kVA (45,000 tons per year of calcium carbide) calcium carbide furnaces at Shandong Bohui Group, a production facility for sodium formate with an annual capacity of 70,000 tons was built. The production line succeeded in its first trial run, and its performance was recognized by relevant experts and end-users; the resulting products achieved high quality and standards. The production process is environmentally friendly, with no secondary pollution and full utilization of resources. It completely ended the history of calcium carbide furnace exhausts being difficult to introduce, hard to purify, and preventing the production of chemical products. Producing sodium formate using furnace gas is equivalent to earning 100,000 yuan in a day. Is there any more detailed information? Where is the company exactly, and can it be visited?
Shandong Bohui Group’s sodium formate production facility has been shut down for a long time; claiming to earn 100,000 yuan per day is just nonsense.
I also heard that Bohui Group has stopped producing sodium formate; the exact reason is unclear. Could someone upstairs let me know?
We can offer an approach to solving the problem of ash accumulation in boilers; first, the issue can be addressed based on technical requirements, and then business matters can be discussed. Put simply, no payment is given if the work isn’t done well. liweipeng139@126.com
Should we continue? Bohui Group stopped producing sodium formate a long time ago; its production technology was very outdated, relying on traditional batch evaporation methods – one batch would be evaporated and then another would be taken out for centrifugal separation. This process was difficult to operate, and when the concentration became too high, it was easy for operators to cause blockages in the evaporator. Nowadays, the DTB continuous crystallization technology is used, allowing for continuous production with simpler operations and a more stable production process.
In addition to being used to produce sodium formate, calcium carbide exhaust gas can also be supplied to the calcination workshops of carbon manufacturing companies as natural gas. Our company pressurizes the calcium carbide exhaust gas and uses it in those workshops for burning carbon blocks, with very good results.
Another use is for burning lime with gas.