JP4594821B2 - Purification method of gasification gas - Google Patents

Description

The present invention relates to tires, a method of combustible wastes such as waste plastics was purified pyrolysis gas obtained by thermal decomposition as fuel gas.

  In general, incineration or landfill disposal methods are generally used for waste treatment. However, in order to effectively use the energy of waste in recent years, the waste is thermally decomposed to combustible gas, tar / light oil, and scattering. A method of obtaining a pyrolysis gas containing char, purifying the pyrolysis gas and using it as a fuel gas has been implemented.

  For example, in Patent Document 1, a carbonization gas (pyrolysis gas) obtained by dry distillation (pyrolysis) of copper-containing organic waste such as shredder dust is mixed with a coke oven gas, and the mixed gas is purified. And the method of utilizing as fuel gas is disclosed. However, when this method is applied to the treatment of wastes rich in volatile matter such as waste plastics, tar in the gas precipitates and solidifies during gas cooling and becomes wax and adheres to and clogs in the piping of coke oven gas purification equipment. This was an obstacle to long-term driving.

  For this reason, it is common practice to wash the gas with water or the like to remove tar, but as described in Patent Document 1, the gas is washed with the waterworks of the steelworks, and the drainage is discharged to the waterworks of the steelworks. In the case of treatment with a treatment facility (activated sludge method), the activity of activated sludge may be hindered by the influence of heavy metals contained in waste water, harmful organic compounds, and the like.

On the other hand, as described in Patent Document 2, there is a method in which organic waste is gasified and then reacted with oxygen and water vapor to reduce tar and light oil in the gas by a reforming reaction. However, if the reforming temperature is about 1100 ° C. or higher, the high-calorie component of the hydrocarbon gas such as methane in the gas is also reduced in molecular weight to H ₂ and CO by thermal decomposition, and the gas calorie is reduced. When gas calorie falls, the range of use as gas becomes narrower. On the other hand, if the reforming temperature is about 1000 ° C. or less, tar and light oil remain in the gas, which is not sufficient.

  Moreover, since the chlorine content contained in the waste is volatilized in the gas as hydrogen chloride, there is a risk of corrosion in the coke oven gas refining equipment and other gas utilization destinations. Furthermore, the chlorine content in the waste causes generation of harmful organic chlorine compounds such as dioxins.

  In this way, especially when wastes rich in volatiles are pyrolyzed and gasified, unless sufficient gas purification treatment is performed on the pyrolyzed gas, organic chlorine such as tar, light oil, dioxins, etc. contained in the gas The compound causes various problems at the gas supply destination.

On the other hand, Patent Document 3 discloses a method of gasifying organic waste and recycling the residue in a blast furnace or a coke oven. However, when waste containing heavy metals or chlorine is treated, Since tar, ash, and char which are residues contain a large amount of organic chlorine compounds such as heavy metals and dioxins, it is not preferable to use them as raw materials for production equipment.
JP 2003-39056 A JP 2004-238535 A JP 2001-221415 A

  The problem to be solved by the present invention is that when high-calorie and volatile-rich waste such as waste tires and waste plastics is gasified to obtain high-calorie gas, tar, light oil, dioxin contained in the gas It is to be able to appropriately remove impurities such as the like.

  Another problem is to effectively use the amount of heat of char and tar generated by thermal decomposition and to prevent environmental pollution caused by organic halogen compounds such as heavy metals and dioxins contained in char and tar.

In the gasification gas purification method according to the present invention, combustible waste is gasified in a pyrolysis furnace, and the pyrolysis gas is reformed in a reforming furnace with oxygen and steam at 700 ° C. to 900 ° C. In a gasification gas purification method for purifying a gas to obtain a fuel gas, the reformed gas is introduced into a first gas cooler, and the gas temperature is 90 to 70 below the adiabatic saturation temperature by water spray or in-liquid combustion. The gas temperature is reduced to 40 ° C. or lower by introducing the gas discharged from the first gas cooler into the second gas cooler and performing heat exchange by direct contact with the cooling water or indirectly heat exchange. Condensed water vapor and light oil vapor, gas introduced from the second gas cooler is introduced into the light oil scrubber, the gas flow rate in the tower of the light oil scrubber is 0.5 to 1.5 m / s, and the temperature of the cleaning oil Is kept 2-3 ° C. higher than the gas temperature, and By contacting the gas with wash oil as 1.0~3.0L / Nm ³ a liquor ratio, benzene contained in the gas, toluene, to absorb light oil components such as xylene wash oil, dioxins in the purified gas After the concentration is 0.1 ng-TEQ / m ³ N (oxygen concentration 12% conversion value) or less, it is mixed with coke oven gas, and further condensed and collected by the first gas cooler and the second gas cooler The product is discharged, the water is separated from the condensed / collected product, and the obtained combustible material such as char, tar, and light oil is returned to the pyrolysis furnace and pyrolyzed again to gasify it, or the pyrolysis furnace It is used as a fuel for supplying a heat source.

In the present invention, the aqueous phase of the first gas cooler and the second gas cooler absorbs acidic gas such as HCl and H ₂ S to remove the acidic gas on the gas side, and the aqueous phase contains NaOH. The pH can be adjusted to a range of 5 to 9 by injecting an aqueous solution such as an aqueous solution (NH ₃ ) as a neutralizing agent.

In addition, for the gas discharged from the second gas cooler, (1) an electric dust collector is installed to remove dust remaining in the gas and mist such as tar, light oil, water, (2) removal A salt / desulfurization tower is installed to absorb and remove HCl and H ₂ S contained in the gas, and the absorbent is neutralized with alkali. (3) A third gas cooler is installed to further increase the gas temperature. It can also be introduced into the light oil scrubber after adding any or all of the gas cooling processes to be reduced.

  Moreover, the trace organic halogen compound in gas can further be reduced by introduce | transducing the gas emitted from the light oil scrubber into an electrostatic precipitator, and removing fine oil mist and a particulate matter.

  In addition, after the gas is heated by a blower booster or an indirect heater on the downstream side of the light oil scrubber, it is passed through an activated carbon packed bed or activated carbon moving bed filled with activated coke or granular activated carbon as activated carbon, and trace amounts of organic halogen such as dioxins The compound can be removed and reduced from the gas by adsorption.

  In addition, as the cleaning oil for the light oil scrubber, it is possible to use the cleaning oil (debensed oil) used for collecting the light oil in the existing coke oven gas refining equipment at the steelworks.

  In addition, distilling and regenerating cleaning oil (ben-containing oil) after absorbing light oil with a light oil scrubber, using existing light oil distillation equipment, separating and recovering waste-derived light oil mixed with coal-derived light oil. You can also.

  In addition, the cleaning oil (ben-containing oil) after absorbing the light oil with the light oil scrubber can be heated and brought into contact with the metal sodium particles to dehalogenate the organic halogen compound contained in the cleaning oil.

  In addition, wastewater generated by condensation during gas purification is sprayed on the heat generated by the gasification process, that is, a pyrolysis furnace, a combustion furnace for external heat, or a secondary combustion furnace that completely burns the combustion furnace exhaust gas. Incineration is desirable, but to improve thermal efficiency or when the raw material has a high water content and cannot be dried and incinerated in the furnace, the generated wastewater is treated with existing low-water activated sludge at the steelworks. Can also be joined.

  In addition, for the wastewater generated in the gas purification process, (1) separation by pressurization of solids, tar and light oil, or separation by specific gravity difference, (2) after cooling the wastewater, alkali is added to the water layer, The pH is adjusted to 9.5 or more and 12 or less, and any or all of separation by coagulating and precipitating the metal contained in the waste water, (3) removal of nitrogen and ammonia by ammonia stripping, is performed as a pretreatment, After the dioxin concentration in the steel is set to 10 pg-TEQ / L or less, the steel plant can be joined to the existing water-reactive activated sludge treatment.

  In addition, as the neutralizing agent used for the first gas cooler make-up water or the first gas cooler and the second gas cooler, use low water produced as a by-product in the existing coke oven at the ironworks. You can also.

According to the present invention, char, tar, light oil, H ₂ S, HCl, HCN, dioxins in pyrolysis gas obtained by pyrolysis even when wastes rich in volatile matter are gasified Impurity content which becomes an obstacle when using such gases can be sufficiently reduced.

  In addition, the combustible material such as char, tar, and light oil separated from the condensed / collected product of the first gas cooler and the second gas cooler is returned to the pyrolysis furnace and again pyrolyzed to be gasified. Or, by using it as a fuel to supply a heat source to the pyrolysis furnace, it is possible to effectively use the amount of heat generated by pyrolysis, such as char and tar, and organics such as heavy metals and dioxins contained in char and tar. Environmental pollution by halogen compounds can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram showing a gasification gas purification apparatus according to the present invention.

  First, a gasification process and a combustion exhaust gas treatment process will be described. In the apparatus shown in FIG. 1, combustible waste rich in volatile matter such as waste tires and waste plastics is gasified. The target object is crushed to a certain size or less in advance by the crusher 1 so that the pyrolysis gasification is completed within the residence time of the pyrolysis furnace 2 and then put into the pyrolysis furnace 2. At that time, depending on the combination of the target and the furnace type, unsuitable materials such as metals and incombustible materials may be included. In this case, unsuitable materials are removed by magnetic sorting, wind sorting, manual sorting, or the like.

  The waste put into the pyrolysis furnace 2 is heated to the pyrolysis temperature by the heat obtained by burning external fuel or the heat obtained by partially burning the waste and consuming its own energy. Generate gas. As a furnace type, a rotary kiln is used in the embodiment, but a shaft furnace, a fluidized bed furnace, and the like can also be used. That is, a method of pyrolysis gasification by external indirect heating such as an external heating kiln or two-column fluidized bed furnace, or a partial combustion method of pyrolyzing waste by partial combustion such as a shaft furnace or fluidized bed furnace Is available.

  In addition, if necessary, wastewater generated in the pretreatment of waste, the purification process of pyrolysis gas, etc. is sprayed on the pyrolysis furnace 2 or the combustion furnace 17 that supplies heat to the pyrolysis furnace 2 to be dried and incinerated. You can also.

  In the case of gasification by external indirect heating, combustion exhaust gas for obtaining a heat source is not mixed on the pyrolysis gas side, so that the calorific value of the pyrolysis gas and the concentration of useful components can be kept high. However, since combustion exhaust gas for obtaining a heat source is generated in a separate system, a separate exhaust gas treatment is required as shown in FIG.

  As a method for treating the exhaust gas of another system, a secondary combustion furnace 3 is provided as necessary, and the temperature and residence time are ensured to a specified value or more to completely decompose dioxins and other unburned components. Further, in the secondary combustion furnace 3, wastewater generated in a pretreatment of waste, a purification process of pyrolysis gas, or the like can be sprayed to be dried and incinerated. As the secondary combustion furnace 3, a furnace shell is often made of a steel plate or a heat transfer tube, and a refractory is lined on the inner surface. In order to promote the decomposition of dioxins, the temperature in the secondary combustion furnace 3 is maintained at a constant level (850 ° C., preferably 900 ° C. or more). The temperature in the secondary combustion furnace 3 is maintained by adjusting the amount of combustion air or the amount of dilution air so that the temperature indication value of a thermometer provided in the furnace becomes a certain target value.

  The gas completely burned in the secondary combustion furnace 3 is introduced into the heat exchanger 4 to recover waste heat. Examples of the heat exchanger 4 include a boiler, a hot water generator, an air preheater, and the like.

  When the waste heat is recovered by the boiler, the obtained steam can be converted into electric power by driving the turbine, and because of the reforming reaction in the stirring gas in the pyrolysis furnace 2 and the reforming furnace 13 described later. It can be used as a water vapor source. The boiler is a natural circulation water tube boiler, and the boiler wall is also used as a heat transfer surface to improve heat recovery efficiency. When the object to be treated is waste containing chlorine and sulfur, the melting point of ash tends to be lowered due to the influence of chlorine and alkali metals contained in the waste. Therefore, there is a possibility that dust adheres to the internal heat transfer tube and heat transfer efficiency is lowered or the boiler is blocked. Therefore, in order to prevent adhesion, a steam-driven soot blower is often provided.

  On the other hand, when waste heat is recovered with a hot water generator, residual heat can be used in nearby facilities. Further, when waste heat is recovered by an air preheater, the heated air can be used as combustion air for pyrolysis in the pyrolysis furnace 2, combustion air in the combustion furnace 17, and the like.

  The heat-recovered exhaust gas is sprayed with water in the exhaust gas temperature-decreasing tower 5, and the gas temperature reaches a temperature (200 ° C. or less) at which dust can be removed by a dust remover 6 (bag filter, electrostatic precipitator, etc.) installed downstream. Is reduced. When a bag filter is used for the dust remover 6, slaked lime or activated carbon can be blown by the blowing device 7 on the dust remover 6 entry side in order to adsorb the hydrogen chloride gas and dioxin contained in the gas.

  Although the exhaust gas is sucked by the induction fan 8, the induction fan 8 is generally installed on the outlet side of the dust remover 6. Thereby, dust troubles, such as dust adhering to the impeller of the induction fan 8 and weight balance breaking, can be prevented.

  The gas whose pressure has been increased by the induction fan 8 is heated to 180 ° C. to 250 ° C. in the exhaust gas reheater 9 (steam indirect heat system, external fuel reheating system, etc.) as necessary, and then the catalyst. The gas is passed through the reaction layer or the activated carbon packed bed 10 and the dioxins and NOx in the gas are decomposed and adsorbed. When NOx is decomposed by the catalyst, high NOx decomposition performance can be obtained by blowing ammonia upstream of the catalyst.

  The exhaust gas gas-treated by the dust remover 6, the catalyst, etc. is diffused from the chimney 11 to the atmosphere. At the chimney 11, an exhaust gas analyzer is installed to monitor the amount of NOx, SOx, HCl, and other air pollutants in the exhaust gas, and chemicals such as slaked lime and ammonia are increased or decreased in accordance with the increase or decrease in the amount of exhaust. The amount of air pollutants emitted can be kept below the specified value.

  Waste-derived dust is collected from the secondary combustion furnace 3, the heat exchanger 4, the exhaust gas temperature reducing tower 5, and the dust remover 6. The collected dust is collected and mixed with chemicals (chelates) in the ash treatment facility 12 and treated as waste, such as disposal at the final disposal site after taking measures to prevent elution of toxic substances such as heavy metals. . Further, when the concentration of heavy metals such as lead and zinc in the fly ash is high, heavy metals can be extracted, concentrated and recycled.

Next, the purification process of the pyrolysis gas produced | generated by the gasification process is demonstrated. As described above, in the apparatus shown in FIG. 1, wastes rich in volatile components such as waste tires and waste plastics are gasified in the pyrolysis furnace 2. A pyrolysis furnace 2 shown in FIG. 1 is an indirect heating type dry distillation kiln and pyrolyzes and gasifies in an oxygen-free state. The pyrolysis products include a liquid component that condenses when cooled to room temperature, a gas component of a gas body even at room temperature, and a solid component as a pyrolysis residue. In the case of a dry distillation kiln, the gas components include flammable H ₂ , CO, and CH ₄ as main components, and in addition, flammable C ₂ to C ₄ hydrocarbon gas and non-flammable CO ₂ and N ₂ are included. The liquid component includes an oil component and condensed water. Oil has distribution from heavy (tar) to light (light oil), and condensed water contains acidic components such as HCl and H ₂ S and NH ₃ . The solid component includes a carbon residue (char) obtained by carbonizing an organic substance into a fixed carbon main body and an incombustible residue mainly including an inorganic component.

  Since combustible waste rich in volatile content such as waste plastic is thermally decomposed in a low temperature range, the pyrolysis product has many oil components such as tar and light oil, and not many gas components. In such a case, the reforming furnace 13 is provided for the purpose of converting the oil component into gas and increasing the gas yield. In the reforming furnace 13, pure oxygen is introduced at a high flow rate through a nozzle, the temperature is increased by heat generated by partially burning the combustible component, and the oil component is thermally decomposed to be converted into gas and char. . At that time, by mixing water vapor with the introduced oxygen, char generation suppression by water gasification reaction, improvement of gasification rate, strengthening of stirring in the furnace, and uniform reaction temperature are achieved.

The reforming temperature is generally in the range of 700 to 900 ° C., the gas temperature at the furnace outlet is measured, and the amounts of oxygen and water vapor are adjusted so that the temperature becomes a target value. By this reforming, tar and light oil are converted to gas such as CO, CO ₂ , H ₂ , CH ₄ , H ₂ O, and char (soot). Setting a high reforming temperature increases the reforming efficiency, reduces tar and light oil content, and also reduces trace amounts of organic halogen compounds such as dioxins, but at the same time, hydrocarbon gases such as methane, ethane, and propane Is also decomposed into CO and H ₂ , so that the gas calorie decreases and the gas volume increases.

  Further, from the viewpoint of thermal efficiency, the steam used for reforming is desirably steam obtained by heat recovery in the heat exchanger 4 (boiler) described above, and the steam temperature is preferably higher (200 ° C. or higher, Preferably 400 ° C. or higher). However, when the temperature is too high, corrosion occurs in the boiler heat transfer tube, so that the steam temperature is preferably about 400 to 450 ° C. However, this is not the case when external fuel is used for the production of steam.

  The hot reformed gas is rapidly cooled by spraying water in the precooler 14 (first gas cooler). Since the reformed gas has a high gas temperature and is unsaturated in water, the sprayed water is instantly vaporized and loses 640 kcal of latent heat of evaporation per kg of water. As a result, the gas is rapidly cooled and cooled to a temperature (70-90 ° C.) slightly below the adiabatic saturation temperature. As the gas temperature decreases, tar having a high boiling point is condensed, and fine char is trapped in water droplets by water spray. As a result, the char and tar are collected at the bottom of the precooler 14 together with the non-evaporated spray water and flow out to the tar decanter 15 (separator). The properties of the collected tar change depending on the water temperature. That is, the tar becomes heavy when the temperature is high, and light when the temperature is low. When tar cools, its viscosity increases and hardens, making handling difficult, and the specific gravity of tar and water is also affected by temperature. Normally, it is experientially adjusted to a cooling temperature of 80 to 85 ° C. and appropriately maintained by steam tracing or the like to maintain the temperature. In the precooler 14, the reformed gas may be rapidly cooled not by water spray but by submerged combustion.

The pyrolysis gas contains acidic gases such as HCl (hydrogen chloride), H ₂ S (hydrogen sulfide), HCN (hydrocyanic acid), NH ₃ (ammonia), alkali salt dust, and water-soluble organic components. Normally, water is acidic with HCl. In order to prevent acid corrosion of the equipment, alkali is added to the spray water (makeup water) of the precooler 14 to adjust the pH, and in order to avoid concentration, it is appropriately blown and diluted. As the alkali, caustic soda, magnesium hydroxide, slaked lime milk, ammonia water or the like is used. In order to appropriately adjust the alkali addition amount, the pH of the circulating water is measured, and the pH is a target value (preferably 5 to 9). ). In addition, when there is a coke oven in the vicinity of the facility, the operation cost can be reduced at low cost by using the low water produced as a by-product in the coke oven as the spray water. Further, when the reforming temperature is high, tar is reduced and char is generated, so that the ratio of tar to char becomes char rich.

  By cooling with the precooler 14, most of the harmful substances (dioxins, heavy metals, etc.) contained in the reformed gas aggregate and become liquid or solid, and tar and char settle in the water at the bottom of the precooler 14 in a turbid state. ,accumulate. However, some of the gas exiting the precooler 14 is scattered as a mist state or a gas state. As a method for reducing such scattering, there are measures such as spraying spray water at a high pressure and reducing the particle size of mist.

  As described above, the char tar collected in the water by the precooler 14 flows out into the tar decanter 15 together with water. Usually, tar has a specific gravity heavier than water and can be separated by scraping the tar that has settled at the bottom of the tar decanter 15. In addition, when the reforming temperature is raised to become char-rich, char is likely to grow in a lump with tar, and the specific gravity is lightened. good. The separated combustible material is once received and stored in the heavy oil tank 16.

  Tar and char separated and recovered from the aqueous phase by the tar decanter 15 and the fixed carbon main body in the pyrolysis residue discharged from the pyrolysis furnace 2 are combustible and can be used as fuel. However, it contains substances that require environmental care, such as chlorine, ammonia, dioxins, and is not suitable as a fuel for production facilities.

  Therefore, in this invention, it utilizes as a fuel of a combustion furnace comprised as a waste incinerator, ie, the fuel or raw material for the pyrolysis furnace 2. Specifically, 1) if the pyrolysis furnace 2 is an indirect heating type as shown in FIG. 1, it is used as a fuel for the combustion furnace 17 that is a high-temperature heat source or as a raw material for the pyrolysis furnace 2, or 2) part If it is a combustion system, it can be recharged into a pyrolysis furnace and thermally decomposed by partial combustion. Thereby, tar char can be effectively recovered as a heat source or gas. Thus, by using by-products as fuel, it is possible to reduce part of the external fuel and waste for the pyrolysis furnace and increase the amount of gas obtained. As a method for separation from the aqueous phase, techniques such as pressure levitation, filter press, and centrifugal separation can be used in addition to a decanter.

  The water from which the char tar has been separated is circulated and used, but in order to prevent the concentration of salts, etc. and the resulting corrosion of the equipment, it is appropriately extracted and blown. Blow water contains solids (SS), oil (n-HEX), dioxins, and the like, so it is once received in an oil / water separation tank 29, which will be described later, and then appropriately discharged and discharged.

  When removal of dioxins is insufficient by gas cooling and gas cleaning by water spray in the precooler 14, a primary cooler 18 (second gas cooler) is installed in the downstream and cooled. The gas temperature is lowered below ℃. When the gas temperature decreases, the gas phase water vapor and light oil rich tar (light oil vapor) are further liquefied by condensation, and the dioxins are dissolved in the water layer and separated from the gas phase. As a result, in the primary cooler 18, the condensed water and tar are separated and recovered, and at the same time, dusts such as dioxins and char can be removed from the gas phase. As an apparatus method of the primary cooler 18, an indirect heat exchange method or a water spray method can be adopted. In the indirect heat exchange system, cooling water of about 15 ° C. to 30 ° C. is allowed to flow through a heat transfer tube installed in the primary cooler 18 to indirectly cool the gas. In the water spray method, cooling water of about 15 ° C. to 30 ° C. is sprayed in the primary cooler 18, and the heat is directly exchanged between the low-temperature water and the gas to cool the gas.

  In the condensed water, the acidic gas component contained in the gas dissolves and becomes strongly acidic and corrosive. Therefore, an alkali chemical is introduced and neutralized so that the pH is 5-9. It is preferable to use caustic soda and aqueous ammonia as the alkali. For this reason, condensed water added with alkali is circulated on the inner wall of the primary cooler 18 and sprayed into the apparatus to wash away the condensed water, thereby preventing the condensed water from becoming acidic. Further, this water spray prevents the light tar component condensing at the same time from growing on the wall and heat transfer tube, and has the effect of capturing and removing dusts and tar mists. As the alkaline water (neutralizing agent) used in the primary cooler 18, the operation cost can be suppressed at low cost by using the water that is by-produced in the coke oven.

  Here, when there is a large amount of char and tar mist remaining in the gas at the outlet of the precooler 14, an electric dust collector (not shown) is installed between the precooler 14 and the primary cooler 18, and dust such as char, mainly light oil It is also possible to remove tar mist and water vapor mist. As a result, the concentration of dioxins in the gas is further reduced, the load of dusts and oils on the downstream primary cooler 18 is reduced, and troubles such as adhesion and blockage on the inner wall can be easily prevented.

  In the embodiment, as shown in FIG. 1, an electrostatic precipitator 19 is provided on the downstream side of the primary cooler 18, and by collecting mist such as dust, tar, light oil, water, etc. contained in the gas, Dioxins are also captured and the concentration of dioxins in the gas is reduced.

  When the object to be treated is waste, since it contains sulfur and chlorine, the gas cooled by the primary cooler 18 contains an acidic gas such as hydrogen sulfide and hydrogen chloride. When acid gas is included, moisture is condensed by cooling during the gas transportation process, and the acid gas dissolves in the condensed water to show severe corrosivity, which causes corrosion troubles in the gas transfer equipment and gas utilization equipment. It happened. Therefore, in the embodiment, in order to prevent corrosion troubles caused by acid gas, a desulfurization / desalting tower 20 is provided to remove acid gas. In the desulfurization / demineralization tower 20, absorption of acid gas is promoted by spraying an absorption liquid into the tower and bringing the sprayed absorption liquid and gas into direct contact. The absorbing liquid is recovered at the bottom of the tower and recycled. Since the absorbing solution shifts to acid with the absorption of the acid gas, the pH is controlled using an alkali. As the alkali, caustic soda, magnesium hydroxide, slaked lime milk, aqueous ammonia, or the like is used, and it is blown appropriately so as not to concentrate salt content by-produced during neutralization and other dissolved components. It is also effective to spray the absorbing liquid in the tower and at the same time install a filler in the tower to improve the contact with the gas.

  Processes such as Takahax, Fmax, Stretford, etc. can be selected as the desulfurization process. If the existing coke oven gas (COG) refining equipment is in the vicinity, the existing equipment is used for the regeneration process of the desulfurization effluent. Can be used. That is, the desulfurization absorbing liquid is supplied from the existing COG gas purification equipment and sprayed into the desulfurization / demineralization tower 20. The sprayed absorption liquid absorbs acidic gas mainly composed of hydrogen sulfide and hydrogen chloride in the gas and stays in the lower part of the tower. The staying desulfurization absorption liquid is sent to the oxidation tower of the existing COG gas purification equipment, and after HS ions are oxidized, it is circulated and reused in the COG gas purification equipment or the above desulfurization / desalination tower 20.

  When ammonia water is used for desulfurization, the gas temperature rises due to reaction heat. The gas temperature also rises when a blower 21 (gas exhauster) is installed before collecting light oil, which will be described later. Since the rise in gas temperature adversely affects the efficiency of collecting light oil, a final cooler 22 (third gas cooler) is provided to reduce the gas temperature. In the final cooler 22, the gas temperature is cooled from about 10 ° C to about 40 ° C. In particular, it is preferable to maintain at 30 ° C. or lower. The cooling method uses an indirect heat exchange method, and the cooling water is recycled. Condensed water containing light oil is generated with cooling, but the condensate is treated by a wastewater treatment method described later.

Gas oil remains in the desulfurized and desalted gas. If gas is supplied in a state where the light oil remains, the gas temperature is reduced by heat dissipation during the transfer of the gas, and the light oil is drained as the gas temperature decreases. Light oil has a low flash point, is difficult to handle, and carries the risk of fire. Therefore, the light oil scrubber 23 is installed to collect the light oil and purify the gas. In the light oil scrubber 23, the cleaning oil is sprayed in the tower, and the gas oil and the cleaning oil are brought into contact with each other to dissolve the light oil contained in the gas in the cleaning oil. Normally, light oil has a high vapor pressure and is oleophilic, and therefore cannot be removed by the primary cooler 18 and the desulfurization / demineralization tower 20, but can be absorbed and removed by using oil as a medium. Usually, oil mainly composed of naphthalene or the like is used as the cleaning oil. In addition, the gas flow rate in the tower of the light oil scrubber 23 is 0.5 to 1.5 m / s, the temperature of the cleaning oil is kept 2 to 3 ° C. higher than the gas temperature, and 5 m ³ / h or more per tower cross-sectional area. A cleaning oil is used, and the gas-liquid ratio is set to 1.0 to 3.0 L / Nm ³ . As the cleaning oil, it is possible to use the cleaning oil (de-bended oil) used for collecting light oil in the existing coke oven gas refining equipment at the steelworks.

  The light oil scrubber 23 collects the cleaning oil (ben-containing oil) that has absorbed the light oil, and the recovered cleaning oil is reused after distilling and separating the light oil in the distillation tower 24. When the facility is in the vicinity of the coke oven gas refining facility, a distillation column of the existing coke oven gas refining facility can be used for the cleaning oil distillation process. In this case, the light oil by-produced in the distillation tower is mixed with the light oil by-produced in the coke oven to produce a product.

  The light oil recovered by the light oil scrubber 23 contains organic halogen compounds such as dioxins. Metal sodium dispersion can be used as a method for decomposing dioxins and the like contained in oil. Specifically, cleaning oil after absorbing light oil heated to about 60 ° C. is put into the decomposition layer, and reaction oil containing metallic sodium particles is mixed. At that time, metallic sodium reacts with organic chlorine bonded to the organic substance to form NaCl. As a result, organic chlorine such as dioxin in light oil is decomposed and removed. In addition, the metal sodium dispersion is mixed with the washing oil in the light oil scrubber 23 and sprayed with the light oil scrubber 23 to promote the desalting reaction in the tower, and the light oil collecting and the desalting treatment can be performed simultaneously. It becomes possible.

  The obtained gas is sent to each usage destination by a blower 25 (gas exhauster). In the embodiment, an activated carbon packed bed or activated carbon moving layer 28 is provided on the downstream side of the blower 25, and dioxins are adsorbed and removed by passing a gas therethrough. Here, activated carbon is activated coke or granular activated carbon. When the gas temperature is lower than the saturation temperature only when the temperature is increased by the blower pressurization, and the condensation of light oil and moisture occurs in the activated carbon packed bed or the activated carbon moving layer 28 where it is easy to cool, the blower 25 and the activated carbon packed bed or activated carbon move. Between the layers 28, a steam indirect heat exchange type gas heater 27 can be provided, and the gas temperature can be raised to a temperature at which the condensation can be prevented. The steam used here is preferably steam generated by the heat exchanger 4 described above. In addition, the activated carbon packed bed or the activated carbon moving layer can be installed on the upstream side of the light oil scrubber 23.

  Further, in the embodiment, the gas emitted from the light oil scrubber 23 is introduced into the electrostatic precipitator 26 before being introduced into the activated carbon packed bed or the activated carbon moving layer 28, and fine oil mist and particulate matter are removed to remove the gas in the gas. Trace amounts of organic halogen compounds are reduced.

Through the above gas purification step, the concentration of dioxins in the gas can be reduced to a reference value (0.1 ng-TEQ / m ³ N (oxygen concentration 12% conversion value)) or less. And when constructing the above-mentioned gas purification equipment in a factory having a COG purification equipment such as a steel mill, by mixing the gas purified through the necessary gas purification process into the COG line, gas delivery to gas Existing infrastructure can be diverted until use.

  Here, by-products (light tar, light oil, char, water) from the primary cooler 18, the electrostatic precipitator 19, the final cooler 22, the refined gas duct, etc. are separated into oil and water in the oil / water separation tank 29, or Dusts such as char and oils such as tar are merged into the tar decanter 15 and used as a heat source in the pyrolysis furnace 2 or the combustion furnace 17 in the same manner as the tar and char separated and recovered from the aqueous phase by the tar decanter 15 described above. It is preferable to use it.

  On the other hand, since water contains many harmful substances and cannot be discharged as it is, it is necessary to perform water treatment. The activated sludge method is the most suitable water treatment method.

  In the embodiment, in the steelworks, the low water activated sludge treatment facility 30 for treating the surplus water from the COG refining process is combined and processed.

  However, wastewater generated during the cleaning process of the pyrolyzed waste gas contains heavy metals such as zinc and lead, various harmful organic compounds, especially organic chlorine compounds such as dioxins, cyanide compounds and benzonitrile. It is difficult to keep the activity high because the activated sludge is contained. Therefore, in order to join the existing low water activated sludge treatment facility 30 and efficiently treat it, it is desirable to remove the inhibitory substance by pretreatment.

  As a pretreatment method, it is effective to apply any one or all of 1) SS separation, 2) coagulation sedimentation, and 3) aqueous distillation.

  SS separation is a technique for separating wastewater containing tar and SS (solid matter) by pressurized flotation or specific gravity difference. Aggregation precipitation is a technique in which the aqueous layer separated by SS separation is cooled, an alkali chemical is added, the pH is adjusted to 9.5 to 12.0, and heavy metals and the like are aggregated and precipitated. Aqueous distillation is a technique for removing nitrogen and ammonia by ammonia stripping of the aqueous layer separated by SS separation. By carrying out any or all of these treatments, the concentration of dioxins in water is set to 10 pg-TEQ / L or less.

  FIG. 2 is a block diagram showing another example of the gasification gas purifying apparatus according to the present invention. In the example shown in the figure, the gas emitted from the primary cooler 18 is purified only by the light oil scrubber 23 in the configuration shown in FIG. In the case where the concentration of dioxins and the like in the gasification gas is low, the concentration of dioxins and the like can be reduced to a reference value or less also in this example, and the equipment is simplified.

  In the example of FIG. 2, the oil / water separation tank 29 in FIG. 1 is also omitted to simplify the equipment, and the condensed and collected products of the primary cooler 18 are joined to the tar decanter 15. Further, the precooler 14 and the primary cooler 18 are sprayed with water.

It is a block diagram which shows the purification apparatus of the gasification gas which concerns on this invention. It is a block diagram which shows the other example of the purification apparatus of the gasification gas which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crusher 2 Pyrolysis furnace 3 Secondary combustion furnace 4 Heat exchanger 5 Exhaust gas temperature reduction tower 6 Dust remover 7 Blowing device 8 Induction ventilator 9 Exhaust gas reheater 10 Catalytic reaction layer or activated carbon packed bed 11 Chimney 12 Ash processing equipment 13 Reforming furnace 14 Precooler (first gas cooler)
15 Tar decanter (separator)
16 Heavy oil tank 17 Combustion furnace 18 Primary cooler (second gas cooler)
19 Electric Dust Collector 20 Desalination / Desulfurization Tower 21 Blower (Gas Exhaust Machine)
22 Final cooler (third gas cooler)
23 Light oil scrubber 24 Distillation tower 25 Blower (gas exhauster)
26 Electric dust collector 27 Gas heater 28 Activated carbon packed bed or activated carbon moving layer 29 Oil / water separation tank 30 Aqueous activated sludge treatment facility

Claims (1)

Gasification of combustible waste gasified in a pyrolysis furnace, this pyrolysis gas is reformed in a reforming furnace with oxygen and steam at 700 ° C to 900 ° C, and the reformed gas is purified to obtain a fuel gas In the gas purification method,
The reformed gas is introduced into the first gas cooler, and the gas temperature is cooled to 90 to 70 ° C. below the adiabatic saturation temperature by water spray or in-liquid combustion,
Steam or gas oil containing a gas temperature of 40 ° C. or less by introducing the gas from the first gas cooler into the second gas cooler and performing heat exchange or direct heat exchange with the cooling water. Condensing steam,
The gas discharged from the second gas cooler is introduced into the light oil scrubber, the gas flow rate in the tower of the light oil scrubber is 0.5 to 1.5 m / s, and the temperature of the cleaning oil is 2 to 3 ° C. higher than the gas temperature. Keeping the gas-liquid ratio at 1.0 to 3.0 L / Nm ³ and bringing the gas into contact with the cleaning oil, thereby absorbing the light oil components such as benzene, toluene and xylene contained in the gas into the cleaning oil,
After the dioxins concentration in the refined gas is 0.1 ng-TEQ / m ³ N (oxygen concentration 12% equivalent) or less, and mixed with coke oven gas,
Furthermore, the condensate / collected matter of the first gas cooler and the second gas cooler is discharged, moisture is separated from the condensate / collected matter, and the obtained combustibles such as char, tar, and light oil are removed. A method for purifying a gasification gas, wherein the gasification gas is returned to the pyrolysis furnace and pyrolyzed again for gasification, or used as a fuel for supplying a heat source to the pyrolysis furnace.

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