KR100967842B1 - Process for producing methane gas using sewage sludge - Google Patents

Abstract

The present invention relates to a process for producing methane gas from sewage sludge.

The present invention also provides a method of increasing the dehydration rate, anaerobic digestion efficiency and methane production of sewage sludge by breaking down the cell walls of sewage sludge and separating the bound water through a continuous heating pressurization reaction.

Sewage sludge, continuous heated pressurized reactor, liquid stripping solution, anaerobic digestion, methane gas, dehydration rate

Description

Method for production of methan gas from sewage sludge

The present invention provides a process for producing methane gas from sewage sludge.

The present invention also relates to a method of increasing the anaerobic digestion efficiency and the methane production of sewage sludge by breaking down the cell walls of sewage sludge and separating the bound water through a continuous heating pressurization reaction.

Waste surplus sludge generated after sewage treatment is an energy source capable of expressing a calorific value of 2,000 to 3,000 kcal / kg upon drying, with a total organic carbon content (TOC, weight%, and drying) of about 20 to 40%. Therefore, in the era of high oil prices, the necessity of energy recycling and the development of new energy resources are needed, and the development of technology that can be utilized as an energy source at the same time as sludge treatment is needed. However, sewage sludge with a water content of about 80% requires expensive energy to remove the cell number (bonded water) during the drying process (hot air drying over 400 ℃), which causes a lot of restrictions in treatment and recycling, resulting in odor. Environmental problems are occurring.

At present, international oil prices are about 110% / bbl, which is about 100% higher than the second half of 2007, and it is an urgent need for energy saving and renewable energy development in the high oil price era. It is expected. In particular, the upcoming taboo on ocean dumping is a risk factor that can lead to a surge in energy consumption while increasing the share of reuse, reduction or fuelization. However, sewage sludge is expected to continue to increase, and the cost of treatment of sewage sludge is expected to increase, which is more inevitable due to the prohibition of dumping at sea. Estimated annual sludge treatment costs (KRW 30,000 / ton) based on 2005 sewage sludge generation amount of 7,052 tons / day are estimated at about KRW77 billion, and oil price increases and ocean dumpings based on 2011 estimates of 9,698 tons / day. Considering the rise in disposal costs due to taboos (W50,000 / tonne), the company is expected to reach W177bn annually.

Therefore, there is an urgent need to develop a technology that can be used as an energy source while treating sewage sludge in an eco-friendly and large-scale.

Sewage sludge is mainly the body of microorganisms having a size of 2 μm, and the material having a viscosity forms flocs to form particles having a size of 100 to 1,000 μm, and a large amount of moisture is contained in the flocs and cell walls.

At present, the biggest problems in sewage sludge treatment are the difficulty of dehydration and drying, low anaerobic digestion rate and high cost. Therefore, there is a demand for development of a method for increasing the low dehydration efficiency and anaerobic digestion rate of sewage sludge and producing methane gas therefrom.

The present invention is to provide a method for increasing the dewatering efficiency and anaerobic digestion rate of sewage sludge, thereby producing a large amount of methane gas from the sewage sludge in a short time.

In addition, the present invention provides a method that can overcome the problems such as the exhaustion of energy resources, high oil prices and carbon dioxide emissions by effectively treating the sewage sludge by producing methane gas from the sewage slurry, and using it as a new energy resource. I would like to.

The present invention, the step of continuously introducing the organic sludge in a heated pressurized reactor, in the reactor for 1 to 3 hours, the reaction temperature is 100 to 300 ℃, the pressure is 1 to 90 kg for a specific temperature value of the temperature range / cm ² Separating the bound water from the cells of the organic sludge by adjusting to be above a certain saturated water vapor pressure within the range, and converting the obtained solid-liquid slurry into methane gas by anaerobic fermentation. It relates to a manufacturing method.

The present invention also provides a method of increasing the anaerobic digestion efficiency and the methane production of sewage sludge by breaking the cell walls of sewage sludge and separating the bound water through pretreatment through the continuous warm pressurization reaction.

By the production method according to the present invention, the dewatering efficiency and anaerobic digestion rate of sewage sludge can be increased, whereby a large amount of methane gas can be produced from the sewage sludge in a short time. In addition, the method according to the present invention provides a method for mass treatment of sewage sludge at low cost, thereby reducing the waste disposal cost of sewage sludge and reducing the environmental pollution caused by sludge disposal, as well as utilizing sewage sludge It provides an additional advantage of producing gas.

The present invention, the step of continuously introducing the organic sludge in a heated pressurized reactor, in the reactor for 1 to 3 hours, the reaction temperature is 100 to 300 ℃, the pressure is 1 to 90 kg for a specific temperature value of the temperature range / cm ² Separating the bound water from the cells of the organic sludge by adjusting to be above a certain saturated water vapor pressure within the range, and converting the obtained solid-liquid slurry into methane gas by anaerobic fermentation. It relates to a manufacturing method.

In the present invention, the production method may further comprise the step of separating the solid liquid slurry into a solid solid and a liquid stripping liquid.

The production method according to the present invention may use a solid-liquid slurry containing a solid solid and a liquid stripping liquid for anaerobic fermentation, or may use only a liquid stripping liquid, but preferably a liquid stripping liquid.

The continuous heating pressurization reactor used in the present invention is to improve the processing time and throughput limitations of the batch treatment device of the Republic of Korea Patent No. 550497, and the problem of energy loss, so that the batch processing device can be continuously operated.

In the production method according to the present invention, the pressure above the saturated water vapor pressure is characterized by being formed by the input pressure of the sewage sludge and the volatilization of the low molecular weight organic material generated in the reactor and the vapor pressure of the water vapor without a separate pressurization device. As a result, the cost of sludge treatment can be reduced because there is no consumption of vaporized energy. The pressure is 1.03 kg / cm ² or more saturated steam pressure at 100 ° C, 4.85 kg / cm ² or more at 150 ° C, 15.85 kg / cm ² or more at 200 ° C and 40.56 kg / cm ² at 250 ° C. It can be set at a specific pressure value of 1.03 to 87.62 kg / cm ² or more for a specific temperature value in the range of 100 to 300 ° C., in the same manner as the saturated steam pressure of not less than, saturated vapor pressure of 87.62 kg / cm ² at 300 ° C.

In the production method according to the present invention, temperature conditions for cell destruction of sludge and separation of bound water are 100 to 300 ° C, preferably in the range of 190 to 250 ° C.

The anaerobic digestion reaction may use a conventional anaerobic fermentation method known in the art. Anaerobic treatment processes in the mesophilic temperature range can achieve higher levels of methanation and treatment stability than thermophilic treatment. Several known anaerobic treatment processes, including anaerobic contact, anaerobic filters, anaerobic fluid beds, bottom-up anaerobic sludge blankets (UASB), and the like, may be used with the present invention for the treatment of hydrolyzate. wind).

In anaerobic digestion reactions, it is generally known that there are four stages involved: hydrolysis, acidogenesis, acetogenesis and methanogenesis, of which the hydrolysis step is known. It is known as a limiting step for sludge digestion, because the cell walls of hard microbes prevent sludge digestion by preventing the escape of intracellular material out of the cell.

The present invention pretreated sewage sludge in a continuous warm pressurized reactor to break the cell wall and separate intracellular bound water, thereby improving the hydrolysis step, which is a limited step in the anaerobic digestion reaction.

Specifically, sewage sludge with a water content of 80% is continuously introduced into a wet pyrolysis (warming pressurization) reactor and pressurized (over 1 to 90 kg / cm ² ) above warming (100 to 300 ° C.) and saturated steam pressure at each temperature. If the reaction proceeds for about 1 to 3 hours, the bound water, which is the moisture contained in the sewage sludge cells, is separated and exists as saturated water in the reactor. This will destroy the sludge cells. When using dewatered sludge (DS) with a water content of 80% as a raw material, a product in the form of a solid (solid + liquid) slurry in which fine particles (about 10 µm in diameter) and a liquid desorption liquid are mixed after the reaction can be obtained. Solid-liquid separation through dehydration means (e.g., dehydrator) can yield solid solids and liquid desorbents with a water content of less than 30%.

In the present invention, the dewatering rate improvement of sewage sludge utilizes the characteristic that the sewage sludge undergoes a hydrothermal pressurization and the cell walls of the cells in the sludge are destroyed so that the cell bound water and the internal water are discharged as free water.

The present invention is designed for high water sewage sludge (water content of 50 to 90%), and it is apparent to those skilled in the art that the present invention can be applied to organic wastes such as food waste having similar properties and desorption liquor, livestock wastewater, and biomass.

The dehydration capacity of the solid-liquid slurry obtained through the continuous hydrothermal pressurization reaction according to the present invention was measured using the CST (Capillary Suction Time) and TTF (Time To Filter) methods. CST is the time it takes for the filtrate of sludge to pass through 1 cm of filter paper through the capillary. The lower the CST measurement, the better the sludge dehydration. TTF represents the time taken for 50% of the sludge volume to exit the filtrate.

The CST results of Table 1 show better results than the results of the batch scale batch reactor under the same conditions. Therefore, the characteristics similar to the batch reaction characteristics, which are ideal reaction conditions, could be confirmed in the continuous hydrothermal reaction.

CST measurement of lab scale batch and continuous hydrothermal reaction products (200 ° C) 1 time Episode 2 3rd time Average lab scale batch 200 ℃ 63.7 64.4 65.4 64.5 Continuous reactor 200 ℃ 46.2 49.7 47.5 47.8

In addition, a similar tendency was also shown in the result of dehydration of TTF, and the results are shown in Table 2 below.

TTF measurement results of lab scale batch and continuous hydrothermal reaction products (200 ° C) 1 time Episode 2 3rd time Average lab scale batch 200 ℃ 93 93 99 95 Continuous reactor 200 ℃ 93 96 93 94

The particle size analysis of the solid-liquid slurry obtained through the continuous hydrothermal pressurization according to the present invention showed a smaller average particle diameter and an effective particle diameter than the batch experiment (see Table 3 and FIG. 2).

Particle size analysis of lab scale batch and continuous hydrothermal pressurization products
By particle size Lab scale batch experiment of sewage sludge Continuous reactor Pilot (1 time) Continuous reactor Pilot (2 times) 200 ℃ 220 ℃ 250 ℃ 200 ℃ 200 ℃ D0.1 5.39 3.18 2.40 2.16 1.68 D0.5 31.23 18.26 12.78 8.34 6.21 D0.9 149.53 54.42 32.92 41.94 32.44

Therefore, from the above results, it was confirmed that through continuous hydrothermal pressurization, the cell wall of sewage sludge was destroyed and the bound water was separated.

In addition, cell wall destruction can be confirmed by increasing the solubilization rate (SCOD / TCOD) of FIG. 3. The breakdown of the cell wall appears to have increased SCOD as the cytoplasm is exposed to the outside. The dissolved organic matter concentration (SCOD: Soluble COD) of the liquid desorption liquid separated from the reaction product of the present invention is 60,000 to 80,000 mg / L on average, and is used as a raw material for the production of methane gas through anaerobic digestion.

In addition, the present invention provides a method for increasing the anaerobic digestion efficiency and methane production of sewage sludge, wherein the sewage sludge has a reaction temperature of 100 to 300 ° C., a reaction time of 1 to 3 hours, and a pressure of the sewage sludge. Pretreatment with a continuous warm pressurized reaction adjusted to be above a certain saturated water vapor pressure within the range of 1 to 90 kg / cm ² for a particular temperature value in the temperature range.

The continuous heating pressurization reactor used in the method includes a closed continuous heating pressurization reactor for accommodating sewage sludge, a stirrer for stirring sewage sludge mounted in the reactor, a temperature sensor for measuring the temperature inside the reactor, Pressure gauge for measuring the pressure inside the reactor, a temperature raising and temperature control device mounted in the reactor, a feed pump for continuously supplying the sewage sludge to the reactor and continuously moving the solid slurry produced in the reactor, installed in the rear end of the reactor Pressure control means for discharging and conveying the product in the form of a solid liquid slurry when the pressure at the rear end of the reactor becomes higher than a predetermined level, and dehydration for separating the discharged and transported product in the form of a solid liquid slurry into a solid product and a liquid stripping liquid. By means of

The sludge is preferably added without drying. Since the sludge is not dried beforehand, the apparatus and time and manpower for drying treatment are not required, and the unit calories of the produced solid-liquid slurry and liquid desorption liquid are also high.

In addition, the warm-up pressurized reactor is operated in a closed state to suppress odor generation.

The reactor may further contain a discharge vessel 15 and a knock-out vessel 16 and an automatic valve attached thereto, in order to release the pressure sequentially in addition to the pressure regulating means as necessary. have.

An example of the continuous wet pyrolysis apparatus is shown in FIG. 1, which is a heated pressurized pyrolysis apparatus that does not require a separate drying process, and is composed of a heated pressurized reactor 13 and peripheral devices in a sealed structure. , Peripheral devices such as hopper (11), feed pump (12), product delivery pipe (14), discharge vessel (15) for two-stage discharge, knock-out vessel (16) for three-stage discharge, solid-liquid separation And dehydration means 17 and heat recovery vessel 18 for steam heat recovery. The continuous wet pyrolysis reactor is a tubular reactor (21), agitator (22), temperature and temperature controller (23), thermometer (24), pressure gauge (25), product partial return pipe (26), product discharge and pressure. Control device 27 and the like.

Embodiments of the present invention are described below, which are merely illustrative to aid the understanding of the present invention, and the scope of the present invention is not limited thereto.

Example 1

sewer From sludge  Preparation of Solid Solids and Liquid Desorbents

A wet pyrolysis reaction was carried out at a temperature of 200 ° C. for 1 ton of sewage sludge (water content: 80%) using a device having the same configuration as the sewage sludge treatment apparatus shown in FIG. 1. The reaction pressure was maintained at a level of 20 atm above the saturated vapor pressure, so that the liquid product did not evaporate, thereby minimizing the consumption of vaporization energy. The solid-liquid slurry produced after wet pyrolysis (water content of 80%) was 285.7 kg of a solid solid having a water content of 30% by a simple dehydration treatment with most of the bound water already converted to free water. On low temperature drying, 210.5 kg of a solid solid having a moisture content of less than 5% was obtained, and 714.3 kg of a desorption solution after dehydration was obtained.

Example 2

Liquid desorption Anaerobic digestion  Efficiency evaluation

In order to evaluate the anaerobic digestion efficiency of the liquid desorption liquid obtained in Example 1, a batch scale digester of 2, 4L double jacketed reactor was constructed. The heating of the reactor was maintained at 35.5 ° C., a mesophilic digestion condition, using a circulating constant temperature water bath, and the temperature inside the reactor (digestion bath) was confirmed using a thermometer.

The mixing inside the reactor used a magnetic stirrer and an agitator. Digestion gas generated in the digester was measured through the digester using a gas collector (gas collector) and a gas meter (gas meter). In addition, the generated gas was analyzed once per hour using GC (HP5890 SERIES II, TCD detector) connected online. Anaerobic digestion microorganisms were sampled from the digestive sludge of Suwon's Environmental Office and used in a stable tank. pH, ORP, temperature and biogas generation were stored in a computer in real time.

The substrate used as a control for evaluating the anaerobic digestion efficiency of the liquid desorption liquid of the hydrothermal pressurization reaction was a concentrated sludge applied to the sludge anaerobic digestion and glucose, which is a representative substrate that is easy to use by microorganisms. All substrates were prepared and added to have the same COD.

The results of the above experiment are shown in FIG. 4, and the best substrates for anaerobic digestion in this experiment are glucose, hydrothermal pressurized liquid stripping solution, and concentrated sludge.

In the case of glucose, biogas is rapidly generated after 24 hours of reaction time and the reaction is completed after 50 hours. Glucose is a substrate that is very easy for microorganisms to use and is thought to go directly to acid production without hydrolysis. Thus, the reaction was completed in 5 days. The hydrothermal pressurized liquid stripping solution showed a slight gas generation up to 120 hours, followed by a rapid gas generation for 30 hours. Therefore, it is considered to go through a hydrolysis step of 5 days. The concentrated sludge used for the anaerobic digestion of the sludge was confirmed that the reaction starts after spending 10 to 15 days, which is the time of the known sludge hydrolysis step. Therefore, the anaerobic digestion time of the sludge can be shortened by 5 to 10 days by solubilization through the hydrothermal reaction.

In addition, it can be confirmed that the amount of the final generated gas also increases. The content of methane in the generated biogas was about 50 to 60%.

As described above, it can be seen that the dehydration rate and the anaerobic digestion efficiency can be increased by pretreatment of sewage sludge with a continuous heating pressurization reaction.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the process of treating sewage sludge used for this invention. The schematic diagram shows a hopper 11, a feed pump 12, a wet pyrolysis continuous reactor 13, a solid-liquid slurry product delivery pipe 14, a discharge vessel 15, a knock-out vessel 16, and solid-liquid separation dehydration. Means (17), heat recovery vessel (18), continuous tubular reactor (21), stirrer (22), temperature raising and temperature regulating device (23), thermometer (24), pressure gauge (25), product conveying pipe (26) And a product discharge and pressure regulator 27.

2 shows the results of particle size analysis of the reaction product of a continuous hydrothermal pressurized pilot plant.

3 is a graph showing the change of solubilization rate (SCOD / TCOD) according to the temperature change of the hydrothermal pressurization reaction product of sewage sludge.

Figure 4 is a graph showing the cumulative results of the generated gas through the anaerobic digestion experiment of the hydrothermal reaction stripper.

Claims (7)

Continuously introducing organic sludge into a warm pressurized reactor; In the reactor, the reaction time is 1 to 3 hours, the reaction temperature is 100 to 300 ° C, and the pressure is 1 to 90 kg / cm ² for a specific temperature value in the temperature range. Separating the bound water from the cells of the organic sludge by adjusting to be above a specific saturated water vapor pressure within the range, and Converting the obtained solid-liquid slurry into methane gas by an anaerobic fermentation method. The method of claim 1, further comprising separating the solid liquid slurry into a solid solid and a liquid stripping solution. The method according to claim 2, wherein the liquid stripping solution is used for anaerobic fermentation. The pressure of any one of the above-mentioned saturated water vapor pressures is based on the input pressure of sewage sludge and the volatilization of the low molecular weight organic substance generate | occur | produced in the said reactor, and the vapor pressure of water vapor | steam without any pressurization apparatus. Characterized in that it is formed. The sewage sludge is continuously adjusted so that the reaction temperature is from 100 to 300 ° C., the reaction time is from 1 to 3 hours, and the pressure is above the specific saturated steam pressure within the range of 1 to 90 kg / cm ² with respect to the specific temperature value in the temperature range. A method of increasing the anaerobic digestion efficiency of the sewage sludge, shortening the anaerobic digestion time, and increasing methane production by breaking the cell walls of the sewage sludge and separating the bound water by continuously entering the formula heating pressurization reactor. The method of claim 5, wherein the continuous heated pressurization reactor, Hermetically sealed continuous heated pressurization reactor for receiving sewage sludge; A stirrer for stirring sewage sludge mounted inside the reactor; A temperature sensor for measuring a temperature inside the reactor; Manometer for measuring the pressure in the reactor; A temperature raising and temperature controlling device mounted inside the reactor; A feed pump for continuously supplying sewage sludge to the reactor and continuously moving the solid slurry produced in the reactor; A pressure regulating means installed at a rear end of the reactor, for discharging and transporting the product in the form of a solid slurry when the pressure at the rear of the reactor becomes above a predetermined level; And Dewatering means for separating the product in the form of discharged and conveyed solid liquid slurry into a solid product and a liquid stripping solution. The method according to claim 1, wherein the solid liquid slurry used for the anaerobic fermentation comprises a solid solid and a liquid stripping liquid.

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