27.65% of coal can be used for coking, which is the basis for the rise of the coking industry.
Blue charcoal is the product obtained by dehydration, rapid pyrolysis and carbonization of Jurassic non-stick coal, long-flame coal and weakly sticky coal at a temperature between 600 and 800 °C. Compared with anthracite and bituminous coal, blue charcoal has The advantages of high fixed carbon content, low volatile content and low sulfur are more widely used in ferroalloy and magnesium metal industries.
With the growth of the scale of orchid carbon, the problem of wastewater treatment of orchid carbon has become increasingly prominent.
Introduction to blue carbon wastewater
1.1 Source of blue carbon wastewater
The pollution of blue carbon wastewater mainly includes three links: low temperature dry distillation, waste gas washing and purification, and blue carbon finished coke quenching.
Waste gas purification wastewater and blue carbon coke quenching water account for the main part of blue carbon wastewater.
As the country vigorously develops the production of clean blue carbon and strictly controls the quality indicators of blue carbon, the coke quenching method of enterprises is gradually replaced by the CDQ process.
1.2 Water quality of orchid charcoal wastewater
Through the monitoring of blue carbon wastewater in different regions: blue carbon wastewater has high pollutant concentration, poor biodegradability, high biological toxicity, color is generally brown or reddish brown and has a pungent odor. The monitoring data range of wastewater from a number of orchid carbon enterprises is shown in Table 1 below.
Due to the incomplete oxidation of coal in the process of blue carbon production, blue carbon wastewater contains a large amount of coal tar and low molecular organic matter.
There are many kinds of organic substances, including phenols, polycyclic aromatic hydrocarbons, benzene series and heterocyclic compounds containing nitrogen, oxygen and sulfur, etc. It is a typical organic refractory industrial wastewater. The following mainly introduces the pretreatment process of blue carbon wastewater.
Blue carbon wastewater pretreatment process
Petroleum, ammonia nitrogen and phenols in blue carbon wastewater have certain economic value and can be recycled.
At present, the basic treatment idea of pretreatment is to recover valuable products in wastewater on the one hand, and improve the biodegradability of wastewater on the other hand, so that the wastewater can be better subjected to biochemical treatment and advanced treatment after pretreatment.
2.1 Oil removal process
The tar in the charcoal wastewater includes heavy oil, light oil and emulsified oil. Heavy oil and light oil can be better separated in the ammonia water circulation tank of the enterprise through gravity sedimentation, but the emulsified oil must be chemically removed. Good removal.
The separated and collected medium and low-temperature coal tar can be combined with the hydrogen produced by the cracking of waste gas to produce the national V standard gas and diesel through the coal tar hydrogenation process.
The degreasing process includes air flotation degreasing, gravity degreasing, chemical degreasing, etc.
Air flotation oil removal will produce more light oil foam, and it is necessary to add chemicals at the front end of air flotation; gravity oil removal cannot remove emulsified oil, and it is more difficult to remove ash mixed in coal tar in a short time.
At present, the degreasing process generally adopts a combination of gravity degreasing and chemical degreasing.
2.2 Deacidification and deamination process
The orchid charcoal wastewater contains a lot of ammonia nitrogen, which cannot be directly biochemically treated.
The ammonia and acid gases in the wastewater are removed from the charcoal wastewater by an ammonia distillation tower. The presence of acid gases at the top of the tower avoids the formation of ammonium sulfate crystallization, but the crystallization problem in the condenser cannot be avoided.
The wastewater after ammonia distillation is slightly acidic, which reduces the acid consumption of the subsequent extraction and dephenolization process.
Organic amines need to be converted into ammonia to the maximum extent through the action of chemicals; at the same time, in order to avoid affecting the operation of the equipment, defoamer is added to suppress the bubbles generated by surfactants and unit phenols.
2.3 Phenol removal process
Phenols in blue carbon wastewater include unit volatile phenols and polyhydric phenols.
Since phenol has an inhibitory effect on the growth and reproduction of microorganisms, the removal of phenol is mainly by physical and chemical methods such as extraction, incineration, advanced oxidation, adsorption and chemical oxidation.
The extraction method utilizes the difference between the solubility of phenol in the insoluble organic solvent and wastewater, and transfers the phenol in the wastewater to the organic solvent for separation. The loaded extractant can be recovered by back extraction (alkali washing) or rectification. Repeated use, but the solvent recovered multiple times will reduce the extraction efficiency.
The incineration method mainly treats high-concentration phenolic water with a phenol concentration of more than 100g/L, but incineration may produce toxic gases; the advanced oxidation method uses strong oxidizing free radicals to mineralize organic matter in wastewater into CO2 and water, but the operation cost is expensive.
The adsorption method includes resin adsorption and activated carbon adsorption, which has the problems of difficult desorption and high material price, and is suitable for low-concentration phenolic water; chemical oxidation method uses strong oxidant to oxidize reducible phenol, and its oxidant consumption is large.
Therefore, phenol is mainly extracted and recovered by adsorption. High-concentration phenol is extracted and complexed, and the remaining low-concentration phenol is enriched by adsorption. Under the premise of meeting the standard, as much crude phenol as possible is recovered, and the use of adsorbent materials is reduced.
With the continuous improvement of environmental protection standards, the difficulty of wastewater treatment limits the survival and development of the orchid carbon industry.
However, the extraction agent recovered in the stripping process of extraction technology is susceptible to pollution, high loss rate, high cost and other factors that restrict the development of the extraction and dephenolization method; the automation of the ammonia distillation tower requires high precision, the condenser is easy to scale, and it is impossible to immediately Factors such as start-stop and other factors affect the wide application of ammonia distillation process; the efficiency of the regenerated adsorbent material decreases.
The spent adsorbent is a hazardous waste, and its disposal is a difficult problem.
Therefore, it is urgent to study new processes, efficient extractants and adsorbents.