0 Introduction
China is the world's coal reserves are more abundant one of the countries, accounting for China's coal reserves of 92.94% of fossil energy, clean coal gasification as an application of technology, in line with China's energy security strategy, in which atmospheric fixed bed gasification technology on its scale of production, the cost of investment, construction period, the line with the majority of metallurgy, chemicals, building materials and machinery industries such as gas demand, especially in two-stage gas furnace used widely.
On the gas station, the phenolic wastewater has been plagued its development's environmental problems, many experts after a long period of research and discussion, phenol removal method for chemical vapor, steam phenol removal method, incineration, solvent extraction dephenolizing France, resins phenol removal method, sulfonated coal adsorption, biochemical dozen phenol water treatment methods have been quite some time application experiments, although groped some effective treatment methods, but also made some effect, but there are many various methods were serious deficiencies, and finally had abandoned. How to take effective measures to completely control wastewater, gas furnace relating to the survival and development.
1 Gas Station phenolic wastewater generated
1.1 Process Gas Station
Two-stage gas furnace gas furnace a high temperature, impurity content of more need to go through purification, cooling, conveying to the gas ignited with Figure 1 is two gas station energy-saving environmental protection technology, the upper gas leaving the gas After pre-furnace decoking decoking and the electrostatic device, remove the gas carrying tar and dust, the following paragraph after the cyclone gas, heat and air-cooled heat exchangers and other equipment, dust, after cooling gas mixed with the previous paragraph. Mixed gas through the electrostatic precipitator and intercooler etc. depth treatment to remove fine dust and gas in some tar, and a small amount of condensation of phenolic wastewater and light oil, and finally by gas pressurization system to the point of use.
Figure 1 two-stage gas furnace cooling Gas Station (environmental protection energy conservation) process
Figure 1 two-stage gas furnace cooling Gas Station (environmental protection energy conservation) process
Chart1 process flow of double stage clean gas station (environmental protection technology)
1.2 Gas Station phenolic wastewater sources
1.2.1 Water entry into
(A) coal water
According to its binding state division, the moisture in the coal can be divided into two kinds of free water and crystalline water, free water was divided into "external water" and "inherent moisture", "external water" influenced by the external humidity. Free water is generally at about 105-110 ℃, after 1-2h after drying escape from the coal, and the water of crystallization is usually to decompose at above 200 ℃ precipitation. Free water in the coal and water of crystallization in the two-stage gas furnace upper distillation section precipitate is dried, mixed with the gas in gaseous form.
(2) water in the gasification agent
Steam as a part of gasifying agent, most of the reaction in the coal gasification combustible material H2, the other part is not involved in the reaction, while the part of the hydrogen in the coal will be converted during the reaction is water, from the gasification The overall result of view, generally in coal gasification reaction of H2 combustible vapor, the gasification agent as the ratio of the amount of steam vapor decomposition rate. It can be seen that high levels of water vapor gasification agent, the decomposition rate of decline will cause steam, gas, water content increases.
(3) fire detection, playing into the brazing operation of the water
Normal gas furnace brazing fight fire detection and accidents during the operation, typically begins with the formation of steam about 0.3MPa steam seal, preventing furnace gas leak, that part will be mixed with the gas in the steam, fire detection or play brazing longer, the greater the amount of water in the mixed gas.
(4) into the ash pan of water seal
Wet gas furnace ash, bottom ash tray at the use of the furnace gas seal from the outside world. High ash fall in the water seal, will be part of the water vapor into the gasification furnace occurs, thereby increasing the water content of the gas.
(5) the gas seal into the water
In the gasifier, in order to more secure, convenient isolation from outside the system of gas equipment or gas pipelines in some place, often set up several water seal, seal surface when the hot gas passing time, will be part of the water vaporized into steam, mixed with coal gas.
1.2.2 the entry of water
(A) coal tar taken out of the water
The gas temperature from outlet of gasifier is controlled at 80-120 ℃, gas in the form of part of the water droplets in the upper section of the primary gas purification system, the gas temperature is further reduced, so that the gas in the droplets increases, and with tar In addition arrested together, mixed with tar.
(2) gas condensate at the intercooler
Double stage producer gas after mixing upper and lower section, the depth of the gas purification intercooler cooling system in indirect heat exchange with the cooling water, the gas is cooled to 35-45 ℃, along with some of the water in gas condensate precipitated this When the gas is saturated.
(3) Gas Pressure Machine drainage
The gas pressurization system, with the gas pressure increases, the partial pressure of water vapor in the gas increase, the gas saturation of the original damaged, the gas resulting in precipitation of some of the water, the water precipitated in part by gas pressure machine drainage systems exclude non-excluded form water droplets into the gas with the gas pipeline.
(4) gas condensate pipeline
Set at the gas pipeline several drainage, the drainage of water from the discharge of two parts, one of which is precipitated in the gas pressurization system but the water drain, and the other part is the gas in the transportation process, the outside Environment cooling or condensing gas pipe wall friction out of the part of the water droplets.
(5) The final water-carrying gas
After purification, cooling, compression, transportation process, some of the water in gas precipitation, and another part, the water droplet-shaped machine with water and saturated water vapor present in the form of gas in the gas point.
1.2.3 Gas Station phenolic wastewater
Gas after purification, cooling, pressure, transmission process, coal tar taken out of the water, gas condensate at the inter-cooler, gas pressure machine drainage, gas condensate pipelines composed Gas Station phenolic wastewater.
1.3 Gas Station production of phenolic wastewater
Gas Station phenolic wastewater yield and moisture content of coal gasification, gasification agent saturation temperature control, fire detection of water vapor pass into the playing time of brazing, gas final cooling temperature, gas pressure, and gas transportation ultimately conveying distance and orientation, and other related piping, and also with the gasification of coal gas production rate, since the higher the rate of gas production, gas is gas into the water at the point of saturation and mechanical more water, condensate out of the relative reduction in the amount of phenolic wastewater. For example: gas station shown in Figure 1 using green energy technology, coal gas production was 3Nm3/kg coal, gasification of coal moisture content of 15%, the saturation temperature and fire detection brazing are playing within the scope of the normal control, gas final temperature is 40 ℃, the gas pressure is 10000Pa, gas as straight conveying, transport distance of 300m, the ambient temperature is 30 ℃, time, Gas Station phenolic wastewater generated per ton of coal gasification is about 160kg or so.
1.4 Gas Station phenolic wastewater main pollutants
Gas Station phenolic wastewater by the phenols, oils, suspended solids and other components, which mainly phenols with monohydric phenols, phenol content, and secondly there is a p-cresol in a two bituminous coal gasification gas station for example, gas phenolic wastewater PH value is generally 7-8.5, the main pollutant index as shown in Table 1.
Table 1 Gas phenolic wastewater pollutant index
(2) Gas Station phenolic wastewater treatment [1,2,3]
2.1 phenolic wastewater pretreatment
The gas station pretreatment method has been applied, about the natural sedimentation separation, mechanical filtration, chemical coagulation method, electrolytic flotation, centrifugation, acid adsorption breaking tar residue, dissolved air pressurized flotation method, several methods such as jet flotation method, evaporation method Gas Station phenolic wastewater treatment process, the phenolic wastewater pretreatment, the use of natural sedimentation separation, multi-stage mechanical filtration and water dilution method are combined , the process see Figure 2, water dilution water injection to maintain system balance evaporation principle of phenolic wastewater pretreatment indicators of major pollutants, as shown in Table 2.
Figure 2 phenolic wastewater pretreatment process
Figure 2 phenolic wastewater pretreatment process
Chart2 process flow of phenol water pretreatment
Table 2 phenolic wastewater pretreatment gas pollutant index
2.2 The final phenolic wastewater treatment
2.2.1 evaporation concentrates
After pretreatment of the phenolic waste water is pumped into the water tank gas furnace, relying on some sensible heat of the waste gas vaporized low boiling phenolic wastewater partially benzene, phenols also will vaporize, the vaporized containing low the boiling point of benzene, phenol vapor steam as a gasifying agent is introduced into the hearth application, the oxide layer occurs furnace temperature is usually about 1100-1200 ℃, at this temperature, benzene, phenols cleaved into water and carbon dioxide. Most higher boiling benzene, phenols are not vaporized, with water tank blowdown, discharged into the tar ponds, waiting for the next stage of processing.
2.2.2 ultimate dephenolizing processing
High concentrations of phenol tar residue is collected in a pool, mixed with coal tar, coal tar extract as benzene, phenol and other chemical raw material, mixed with one of the phenolic wastewater residue of benzene, phenols increased tar value in use. Tar can also be used as a fuel, this time, one of the phenolic wastewater mixed with the residue of benzene, phenols and other toxic substances along with tar burning, at 1100-1200 ℃ conditions, cleavage of H2O and CO2 into the atmosphere The main reaction equation is C6H5OH +7 O2 = 6CO2 +3 H2O. Two gas station phenolic wastewater evaporation method ultimately control process shown in Figure 3.
Figure 3 phenolic wastewater treatment process ultimately evaporation method
Figure 3 phenolic wastewater treatment process ultimately evaporation method
Chart 3 final process flow of evaporation condensing method to deal with phenol water
3 Gas Station phenolic wastewater treatment issues related to analysis
3.1 phenolic wastewater treatment effect
Gas Station phenolic wastewater containing phenol concentration is low, not directly to the recovery of benzene, phenol, combined gas furnace gasification characteristics, the use of phenol wastewater evaporation method to govern, both the use of phenolic wastewater in the water, and completed phenol solution was concentrated and refined by professional chemical plant, the process fully reflects the concept of waste resource management, the effective realization of the gas station energy-saving and emission reduction, with a more significant economic and environmental benefits.
3.2 Device scaling problems [4]
Waste gas cooling process of phenol condensate, the water will form a hard scale box wall; phenol after pretreatment of wastewater and suspended solids content of less oil, oil is light oil, fine particle suspension , both easily deposited in the water, another blowdown operating system, you can effectively prevent the formation of dirt.
3.3 equipment corrosion problems [4,5]
Wastewater evaporation system is fully enclosed, and the limited amount of dissolved oxygen in wastewater, thus effectively avoiding the dissolved oxygen caused by electrochemical corrosion; wastewater evaporation process at high temperature, the water no microbes, bacteria and algae to survive, there is no micro-organisms Corrosion caused; phenol wastewater itself chloride and sulfate ion content is very low, water pretreatment process, without adding any processing agents, no increase in chloride ion, a sulfate ion salts and other harmful ions, water evaporation process, Corrosion caused harmful ions is very small; gas station two phenolic wastewater PH value is generally between 7-9, less corrosive.
4. Epilogue
Gas station phenolic wastewater treatment, has been troubled by the application of producer gas development priority environmental problems, the use of gas sensible heat of evaporation wastewater, the waste heat recovery, waste water recycling and phenolic wastewater treatment technology to combine the contained phenolic wastewater and resource utilization, the effective realization of the gas station energy-saving and emission reduction, with a more significant economic and social benefits.
