1 Several methods of activated carbon regeneration
1.1 Chemical method for drug elution
For high-concentration, low-boiling organic matter adsorbates, chemical regeneration should be considered first.
(1) Regeneration of inorganic agents. It refers to the removal of adsorbate by a chemical such as inorganic acid (sulfuric acid, hydrochloric acid) or alkali (sodium hydroxide), also known as acid-base regeneration. For example, carbon adsorbing high concentration of phenol is washed with sodium hydroxide solution, and the desorbed phenol is recovered as sodium phenolate. The regeneration process is shown in FIG. The carbon which adsorbs heavy metals in the wastewater can also be regenerated by this method, and the regenerating agent uses HCl or the like.
(2) Organic solvent regeneration. The organic matter is dissolved by benzene, acetone and methanol to extract the adsorbate adsorbed on the activated carbon. The regeneration process is shown in Figure 2. For example, carbon adsorbing high concentrations of phenol can also be regenerated with an organic solvent. The saturated charcoal treated with activated carbon in the coking plant gas washing wastewater can also be regenerated with an organic solvent.
Chemical regeneration method using chemical elution sometimes recovers useful substances from the regeneration liquid. The regeneration operation can be carried out in the adsorption tower. The loss of activated carbon is small, but the regeneration is not complete, the micropores are easily blocked, and the recovery of adsorption performance is affected. Rate, the adsorption performance is significantly reduced after repeated regeneration.
1.2 Biological regeneration method
The domesticated activated carbon is used to treat the spent activated carbon, and the organic matter adsorbed on the activated carbon is degraded and oxidatively decomposed into CO 2 and H 20 to restore its adsorption performance. The method for regenerating saturated carbon by using microorganisms is only suitable for adsorbing susceptible microorganisms. The carbon of the decomposed organic matter is saturated, and the decomposition reaction must be thorough, that is, the organic matter is finally decomposed into CO 2 and H 20 , otherwise there is a possibility of being adsorbed by the activated carbon. If the treated water contains organic matter that is difficult to degrade or hard to desorb, the biological regeneration effect will be affected.
In recent years, the strong adsorption characteristics of activated carbon to organic matter and dissolved oxygen in water, and the surface of activated carbon as a good carrier for microbial aggregation and growth, under the appropriate conditions, simultaneously exert the adsorption of activated carbon and the biodegradation of microorganisms. The water treatment technology is called Biological Activated Carbon (BAC). This method can make the use cycle of activated carbon many times longer than the usual adsorption cycle, but after using for a certain period of time, the part that is adsorbed by activated carbon and difficult to biodegrade will still affect the effluent quality. Therefore, in the deep treatment of drinking water, too long an adsorption cycle of activated carbon will be difficult to ensure the quality of the effluent, and regular replacement of activated carbon is necessary.
1.3 Wet oxidation method
This regeneration process is commonly used to regenerate powdered activated carbon, such as powdered charcoal added to enhance aeration tank processing capabilities. The adsorbed saturated carbon slurry is heated to 200-250 ° C, and pressurized with air to (300-700) X104P, and the organic matter adsorbed by the activated carbon in the reaction tower is oxidatively decomposed under high temperature and high pressure to regenerate the activated carbon. The regenerated carbon is cooled by a heat exchanger and sent to a carbon storage tank for reuse. The ash after carbonization of the organic matter is periodically discharged after being accumulated at the bottom of the reactor.
The wet oxidation method is suitable for treating adsorbent substances with high toxicity and biodegradability. The temperature and pressure must be determined according to the characteristics of the adsorbate, as this directly affects the recovery rate of carbon adsorption performance and the loss of carbon. The regeneration system of this regeneration method has many auxiliary facilities, so the operation is troublesome.
1.4 Electrolytic oxidation
The organic matter adsorbed by the activated carbon is oxidatively decomposed by using a strong oxidant such as [O], [C1], which is generated during electrolysis. However, in actual operation, there are problems such as corrosion, passivation, and clogging of metal electrodes. Insoluble electrode--Graphite has the disadvantages of large volume, high electrical resistance, high power consumption, etc., so it has not been applied in practice.
1.5 Heating regeneration method
According to the temperature at which the organic matter decomposes and desorbs during heating, the heating regeneration is classified into low-temperature heating regeneration and high-temperature heating regeneration.
(1) Low temperature heating regeneration method. For the saturated carbon which adsorbs a low molecular weight hydrocarbon having a low boiling point and an aromatic organic substance, the carbon is generally regenerated by steam blowing at 100 to 200 ° C, and regeneration can be carried out in the adsorption tower. The desorbed organic vapor can be recycled after being condensed. Activated carbon regeneration commonly used for gas adsorption. The steam stripping method is also used for the regeneration of saturated activated carbon for the pre-treatment of process water in the beer and beverage industries.
(2) High temperature heating regeneration method. In the water treatment, the activated carbon adsorbs mostly thermal decomposition type and hardly desorbed organic matter, and the adsorption cycle is long. The high-temperature heating regeneration method is usually heated at a high temperature of 850 ° C, so that the organic matter adsorbed on the activated carbon is carbonized and activated to achieve the purpose of regeneration, the adsorption recovery rate is high, and the regeneration effect is stable. Therefore, high temperature heating is generally employed for the regeneration of activated carbon for water treatment.
After dehydration of activated carbon, the whole process of heating and regeneration generally goes through the following three stages.
(1) Drying stage. The wet carbon having a water content of 50% to 86% is heated at a temperature of 100-150 ° C to evaporate the adsorbed water in the carbon particles, and at the same time, some of the low-boiling organic substances are also volatilized. The heat consumed in this stage accounts for 50% to 70% of the total energy consumption during the whole process of regeneration.
(2) The roasting stage, or carbonization stage. The pelletized carbon is heated to a temperature of 150 to 700 °C. Different organic substances are eliminated from the matrix of activated carbon in the form of volatilization, decomposition, carbonization and oxidation as the temperature increases. Usually, at this stage, the recovery rate of recycled carbon has reached 60% to 85%.
(3) Activation phase. After the organic matter is carbonized at a high temperature, a considerable portion of the carbide remains in the activated carbon micropores. At this time, the carbide needs to be gasified by an oxidizing gas such as steam or carbon dioxide, and the residual carbide is vaporized to a gas such as CO 2 or CO at about 850 ° C. The surface of the micropore is cleaned to restore its adsorption performance.
The reaction formula of residual carbides and oxidizing gases is as follows:
C + O2 → CO2↑
C + H2O → CO↑+H2↑
C + CO2 → 2CO↑
During high temperature regeneration, oxygen has a great influence on the matrix of activated carbon, so it must be operated under micro-positive pressure conditions. Excessive oxygen will cause the activated carbon to burn and ash, while too low an amount of oxygen will affect the furnace temperature and regeneration effect. Therefore, the oxygen in the general high-temperature heating regenerator must be strictly controlled, the residual oxygen content is less than 1%, the CO content is about 2.5%, and the steam injection amount is 0.2-1 kg/kg activated carbon (determined according to the furnace type).
The advantages and disadvantages of activated carbon regeneration equipment are mainly reflected in: adsorption recovery rate, carbon loss rate, strength, energy consumption, auxiliary material consumption, regeneration temperature, regeneration time, impact on human body and environment, equipment and basic investment, operation management and maintenance degree.
In addition, any activated carbon high-temperature heating regeneration device needs to be properly solved to prevent carbon particles from sticking to each other, sintering into blocks and causing local fire or blockage of passages, and even causing running defects.
Eps Sandwich Panel,Sandwich Panel,Insulated Panel
Steel Structure,Sandwich Panel Co., Ltd. , http://www.nsprefabhouse.com