Methane gas generator

Abstract

To develop manufacturing of methane gas having high concentration with reduced energy.SOLUTION: Gas purification is enabled by pressurizing and supplying a mixture of raw refuse, excreta, and sewage sludge to a methane fermentation tank by a feed water pump, and using a pressure of gas generated after fermentation.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methane gas generator (hereinafter referred to as "this device") for a system and method of pressurizing a mixture of food waste, sewage sludge, excrement, etc. with a pump, fermenting it in a methane fermentation tank, and purifying the generated mixed gas such as methane and carbon dioxide for use.

Background Art

[0002] Conventionally, in Japan, most of the household and general waste has been incinerated in its entirety at waste incineration facilities, discharging a large amount of exhaust gas. In response to the international convention concluded at the 1992 "Earth Summit" to prevent the emission of greenhouse gases on a global scale to prevent global warming, at sewage treatment plants and waste incineration plants, sewage and general waste are crushed and separated to separate food waste, and at sewage treatment plants, sewage is methane-fermented and the gas is supplied as fuel for a gas engine without being purified to a methane concentration of about 60%. Since it contains about 40% carbon dioxide in addition to methane and saturated moisture, it is not suitable as fuel for an internal combustion engine. As a result, the power generation efficiency is as low as around 30%, and the rest is dissipated as heat into the atmosphere.

[0003] The methane gas with a methane concentration of 60% and saturated moisture as described above has no sales route as fuel, and most municipalities, which are gas manufacturers, have no choice but to sell the gas to power generation operators.

[0004] As a mixed fermentation device for food waste and sewage sludge, there is Patent Document 1. Although this method enables efficient methane fermentation, it is necessary to boost the pressure of the gas for purifying methane because the fermentation gas is under atmospheric pressure. However, after the gas is generated, its volume expands by more than 100 times compared to the liquid of the raw material, and a large amount of power is required for gas compression.

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Food waste increases from spring to summer, and the composition of food waste varies depending on seasonal fluctuations, regions, such as towns and villages or urban areas. In terms of weight, food waste is overwhelmingly more, and sewage sludge and excrement are less than food waste, but food waste alone has less nutrition for fermenting bacteria, less mineral content, and a slower fermentation rate. It is necessary to add an appropriate amount of sewage sludge and excrement to accelerate fermentation and stabilize fermentation.

[0007] The generated methane has a low calorific value at a concentration of about 60%, is saturated with moisture, and has a low commercial value. It is necessary to increase the commercial value as dry methane with a methane concentration of 99% or more at low cost.

[0008] To purify low-concentration methane at atmospheric pressure shown in Patent Document 1, a gas compressor for pressurization is required, and a large amount of electric power is consumed to boost the pressure to the required pressure.

Means for Solving the Problems

[0009] If a mixture (hereinafter referred to as the mixture) in which the flow rates of excrement and sewage sludge are adjusted to be optimal for fermentation based on the weight of food waste is pressurized with a water supply pump after mixing and supplied to the fermentation tank, the volume is small, and methane fermentation is possible with a small power.

Effects of the Invention

[0010] If methane is generated under pressure and gas purification is carried out using the pressure of a mixed gas such as methane and carbon dioxide, it becomes possible to produce high-concentration methane gas by itself, energy saving, and the purified methane gas can be developed for fuel sales. In recent years, due to the problem of global warming, there is also a possibility of sales as biofuel.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the actual embodiment of the invention of this device will be described with reference to Fig. 1. Sewage sludge 1 can be constantly supplied through a sewer pipe, but night soil 2 is intermittently supplied by a vacuum truck and stored in a sewage and night soil temporary tank 3 after garbage and the like are removed. On the other hand, food waste 4 is transported to a garbage storage tank 6 by a garbage collection truck, finely crushed by a crusher 7, and then sorted by a sorter 8. Plastics and the like that do not ferment are carried out of the system from a temporary storage tank 9. The sorted food waste is transported to a mixing tank 11 by a belt conveyor 10 or the like, mixed with the above-mentioned sewage sludge 1 and night soil 2, pressurized by a feed water pump 13 via a filter 12, and supplied to a fermentation tank 14 to ferment, generating methane gas, carbon dioxide, etc.

[0013] Explanation of the attached (Table 1), Regarding gas purification, 1. A mixture of food waste, sewage sludge, etc. is pressurized by a feed water pump 13 and

Table 1

[0014] Other explanations, If a sufficient installation area can be secured for the methane fermentation device, installing a solar panel 31 enables power supply to the feed water pump 12 and the like.

[0015] [Fig. 1] shows the flow of this device. The practical embodiment of the present invention is shown in FIG. 1, and gas purification by membrane separation is shown in FIGS. 2 and 3. The raw sewage sludge 1 is constantly supplied, but the night soil 2 is intermittently supplied by the vacuum truck 3 and stocked in the temporary storage tank 4. The food waste 5 is stored in the food waste storage tank 6 by the garbage collection truck, then subdivided by the crusher 7, and then sorted into fermented and non-fermented substances by the sorter 8. Plastics and the like are sent out of the system as non-fermented substances 9. Thereafter, the food waste 5 is premixed with the aforementioned sewage sludge 1 etc. in the premixing tank 11 by the conveyor 10 to become liquid, and is pumped into the methane fermentation tank 14 by the feed water pump 12 and fermented. Since the fermentation gas contains ammonia, it is desulfurized by the alkaline water 22 of the desulfurizer 21. Thereafter, after removing the mist contained in the drain separator 24, it is heated to an optimum temperature for gas separation by the heater 25 to become the raw material gas 26.

[0016] The electric power generated by the solar power generation panel 31 can drive the feed water pump 12 etc., and supply fuel to the users of methane gas in the vicinity in case of disaster.

[0017] Membrane separation is shown in FIGS. 2 and 3 as the gas separation method. In addition to this, there is the adsorption method for gas separation, but membrane separation is convenient as gas separation that does not require moving parts. In FIG. 2, the aforementioned treated gas 26 is supplied to the membrane 32, and mainly carbon dioxide and moisture contained therein permeate to become the permeated gas 35. The methane component that has permeated through the membrane is reused as the combustion aid of the aforementioned boiler 27. FIG. 3 is a system in which methane permeated from the previous primary membrane 32 is recovered and compressed by the gas compressor 36 and then recovered again by the secondary membrane 37 when the methane concentration and methane recovery rate are higher than those in the case of FIG. 2. If methane is recovered excessively, the heat quantity for maintaining the fermentation in the fermentation tank 14 will be insufficient. Therefore, either of FIGS. 1 and 2 is selected according to the heat balance such as the heat dissipation ratio with the outside air temperature etc. In order to continue the fermentation, the product gas 34 and the permeated gas 35 are supplied as fuel to the boiler 27, and the generated steam or hot water 28 is supplied to the aforementioned heating coil 17 to heat the fermentation liquid 15 and continue the methane fermentation.

Industrial Applicability

[0019] Other explanations If sufficient installation area can be secured for the methane fermentation device, power can be supplied to the water supply pump 12, etc. by installing the solar panel 31 on the site.

[0020] [Figure 1] 1 Sewage sludge 2 Night soil 3 Vacuum truck 4 Temporary storage tank 5 Food waste 6 Food waste storage tank 7 Crusher 8 Separator 9 Non-fermentable material tank 10 Conveyor 11 Premixing tank 12 Filter 13 Water supply pump 14 Methane fermentation tank 15 Fermentation broth 16 Heat preservation 17 Heating coil 18 Stirrer(s) 19 Monitoring instrument(s) 20 Residue 21 Desulfurizer 22 Alkaline water (in) 23 Alkaline water (out) 24 Drain separator 25 Heater 26 Raw material gas for gas separation 27 Boiler 28 Steam or hot water 29 Burner 30 Exhaust 31 Solar power generation panel [Figure 2] 32 Primary membrane 33 Metering valve 34 Product gas 35 Permeate gas [Figure 3] 36 Gas compressor 37 Secondary membrane 38 Collection point

Claims

1. This methane gas generator is used at a treatment plant where sewage sludge, human waste, food waste, etc. are used as raw materials in a methane fermentation tank where the raw materials are fermented into methane. The system includes a feedwater pump that pressurizes the raw materials to 5 to 9 atmospheres after pre-mixing and supplies them to the fermentation tank, a fermentation tank, ammonia in the fermentation gas, a drain separator, a heater, a gas purification device, and a boiler to continue fermentation.

2. 2. A methane gas generator having a gas purification function by a membrane method or an adsorption method, utilizing the gas pressure of 5 to 9 atmospheres generated in accordance with claim 1.

3. 2. A methane gas generator according to claim 1, wherein the power consumed by the methane gas generator is powered by solar power.

Images