Patent Application
20140206056
The present invention relates to apparatuses, such as small and medium scale processing plants, for conversion of biomass into methane and other high-grade products such as fertiliser. The present invention further relates to methods and uses of the present apparatuses for conversion of biomass into methane and other high-grade products such as fertiliser.
In the Netherlands, the average annual production of biomass is approximately 30,000 tonnes dry matter of which nearly 28,000 tonnes is produced in agriculture. This tonnage represents an energy content of 475 pJ of renewable energy each year equal to 15 billion m3 natural gas. In comparison, in the Netherlands, the use of natural gas was 1400 pJ in 2008.
Part of the annual biomass production is used as marketable products, or raw materials, while the remainder is not, or scarcely, used. A large portion of the annual biomass production which is used eventually results in organic waste streams, and especially wet organic waste streams, such as liquid manure, manure, sewage sludge, domestic vegetable waste, agricultural plant residue or domestic plant residue.
The energy content of the primarily non-used biomass and the organic waste streams of the primarily used biomass is considerable in addition to nutrient content, for example, nitrogen, phosphor, minerals and trace elements.
Conversion of non-used biomass, such as agricultural and forestry waste and organic waste streams of the primarily used biomass into high-grade products, for example natural gas, can significantly contribute to the amount of sustainable energy, or green energy, available for energy consumption and, accordingly, significantly contribute to reduction of green house gasses such as CO2.
It has been estimated that 30% to 60% of the annual biomass production can be converted into methane or natural gas thereby, for example, providing a renewable potential alternative for 10% to 20% of the natural gas consumption in the Netherlands.
Conversion of organic waste streams, and especially manure, into methane has been used for decades. The most commonly used method basically comprises a large air-sealed holder in which manure is collected and allowed to ferment, i.e. convert or digest, carbon based or organic materials into methane, generally for 30 to 40 days. The resulting (bio)gas generally comprises approximately 40% CO2, 60% methane and changing amounts of H2S.
In principle, the (bio)gas produced is not directly suitable for energy consumption because, amongst others, its relatively low methane content. Additionally, the presence of large amounts of CO2 and H2S is undesired in an energy source.
In practice, it is been shown that fermentation of manure alone does not suffice to efficiently convert manure into methane. The addition to the manure of additional nutrient sources such as maize is required to aid the fermentation process.
Further, in practice, it has been shown that only large scale biogas production facilities can be economically exploited for biogas production. On site small scale plants using locally produced biomass are not feasible from an investment and production yield point of view.
An additional problem associated with traditional natural gas, or methane, production using biomass is the residue obtained after fermentation. This residue comprises high concentrations of microorganisms, besides ammonia, heavy metals, phosphor and nitrogen, and is not directly suitable to be used, for example as a fertiliser, and, accordingly has to be further processed or disposed thereby, amongst others, increasing the costs of the traditional biogas production process.
A further problem especially associated with organic waste streams produced by animals, such as (liquid) manure, is the annual release of NH3, or ammonia, in the environment, for example by discarding the manure or directly using it as fertiliser. The discarded animal organic waste streams also significantly contribute to the additional direct release of methane, a green house gas, in the atmosphere.
Although the problems associated with renewable natural gas, or methane, production from biomass have been described above especially in relation to manure conversion into biogas, most of these problems, such as inefficient conversion, low-grade biogas, not feasible on a small scale, are also associated with other organic waste streams such as sewage sludge, domestic vegetable waste, agricultural plant residue or domestic plant residue.
Especially for small scale conversion of biomass, a biomass conversion plant, or installation, preferably meets most, if not all, of the requirements presented below:
Especially for medium scale conversion of biomass, a biomass conversion plant or installation preferably meets most, if not all, of the requirements presented below:
It is an object of the present invention, amongst other objects, to provide apparatuses, or installations or plants, for conversion of biomass into methane and other high-grade products meeting at least part, if not all, of the above requirements for small scale (local) and/or medium scale (regional) production facilities of natural gas and other high-grade products.
The above object, amongst other objects, is met by an apparatus for conversion of biomass as defined appended claim 1.
Specifically, the above object, amongst other objects, is met by an apparatus for conversion of biomass, the apparatus comprises:
The present inventors have surprisingly found that the above combination and order of separate reactors operated under the conditions specified, provides:
The present reactors (1) to (4) are based on microbial conversion, or processing, of biomass. The microorganisms, such as fungi and bacteria, used in the reactors can be provided by, or present in, the biomass itself, or can be inoculated in the reactors at, for example, start-up of the apparatus. Suitable inoculation cultures can be found in waste and surface water purification installations.
According to the present invention, selection of species of microorganisms is not particularly important. The reaction conditions defined allow the creation of specific environments favouring the growth and/or phenotype of acid producing microorganisms, such as fungi, in the acidification reactor (1), production of methane, for example by bacteria, in the methane synthesis reactors (2) and (3) and the nitrification in the nitrification reactor (4).
The present acidification reactor (1) of a mixed fluid type reactor substantially provides acidification by acid secretion of microorganisms. However, for example, when the biomass supplied comprises a high nitrogen content, the indicated pH range can be optionally maintained by adding additional sugar or acid to the biomass or into the reactor (1).
The present inventors have surprisingly found that by microbial acidification of the biomass under the conditions specified:
If present, contaminants such as plastics can be readily removed from the process stream by separation, or isolation, of the surface layer.
The above phase separation allows separating sludge and liquid process flows using traditional techniques such as sedimentation, filtration, tilted plate separators, or crossflow microfiltration. Additionally, separated sludge and liquid flows prevent clogging of the apparatus and allow efficient heat-exchange providing a reduction of external heat required by 60% to 70%.
After acidification of the biomass, the acidified biomass is transported to and discharged in a methane synthesis reactor (2) allowing separation of the acidified biomass in a sludge and liquid stream. The acidified sludge biomass is subjected to an anaerobic environment allowing microbial methane production and the acidified liquid biomass is discharged into a methane synthesis reactor (3) where it is separately subjected to a similar anaerobic environment allowing microbial methane production.
Thereafter, the processed liquid biomass is transported to and discharged in a nitrification reactor (4). Under the conditions specified, the nitrification reactor (4) microbially converts NH4+ (NH3) into non-gaseous NO3− thereby lowering the pH of the processed liquid biomass to a pH of 6.5 to 7.5 resulting in a directly useable, for example as a liquid fertilizer solution, neutral mixture of ammonium nitrate and urea.
The present inventors have surprisingly found that the apparatus as described above allows conversion of biomass in 1 to 2 days, in comparison, the traditional plants require 30 to 40 days, with an efficiency of conversion of 80 to 85% per day or more.
Without being limiting to the invention because of an underlying mechanism, at least a substantial part of the efficiency of the present apparatus with respect to methane production appears to be attributable to high concentrations of acetic acid in the acidified liquid biomass.
According to a preferred embodiment of the present invention, the present acidification reactor (1) further comprises an outlet for discharging H2S comprising gaseous effluent and the apparatus further comprises:
The present inventors have surprisingly found that the gaseous effluent of the acidification reactor (1) substantially comprises a substantial amount of, if not all, sulphur in the form of H2S present in the biomass supplied. Accordingly, substantially all sulphur, or at least a significant portion thereof, can be conveniently removed in a early stage of the conversion process by discharging the gaseous effluent from the acidification reactor (1).
By transporting and discharging the gaseous effluent in the present effluent gas conversion reactor (5) and subjecting it to the condition specified, microbial conversion of gaseous H2S into SO4− salts is obtained.
Acidic liquid comprising SO4− discharged from the effluent gas conversion reactor (5) can be conveniently used in the apparatus for pH regulation.
According to another preferred embodiment of the present invention, the apparatus for conversion of biomass comprises:
The present composting reactor (6) receives processed sludge biomass from the methane synthesis reactor (2) and subjects the sludge to the indicated conditions for a period of time sufficient for drying and further digestion, such as for 10 to 30 days.
The controlled oxygen pressure and relatively high temperature ensures efficient composition. In addition, at least partially performing the process at temperatures above 70° C. allows for decontaminating the compost of most potential pathogenic microorganisms.
Since the input stream of the composting reactor (6) is low in sulphur, sulphur is removed in the acidification reactor (1), but high in minerals and trace elements, the resulting composted biomass is a high-grade directly usable fertiliser.
If present in the biomass, heavy metals can be readily removed by subjecting the acidified or processed sludge biomass to a sedimentation step and removing the sediment comprising heavy metals from the process stream(s).
According to yet another preferred embodiment, the present invention relates to an apparatus for conversion of biomass wherein the composting reactor (6) comprises a further outlet for discharging acetate comprising leachate and the acidification reactor (1) comprises a further inlet for receiving the acetate comprising leachate.
Acetate or acetic acid comprising leachate is produced in the composting reactor (6) as a hydrolyzation product of cellulose. Because of the relatively mild acidic nature of acetic acid, in addition to its buffering capacities, the leachate produced by the composting reactor (6) can be transported to, and discharged in, the acidification reactor (1) thereby assisting in maintaining the pH in the required range.
Gaseous effluent from the composting reactor (6) comprising NH3 can be conveniently processed in the nitrification reactor (4).
According to still another preferred embodiment, the present invention relates to an apparatus wherein the methane synthesis reactor (2) comprises a phase separation device for separating the acidified biomass into an acidified liquid biomass and an acidified sludge biomass comprising at least one inlet for receiving acidified biomass and at least two outlets for discharging acidified liquid biomass to the methane synthesis reactor (3) and acidified sludge biomass and a methane synthesis device comprising at least one inlet for receiving the acidified sludge biomass and at least one outlet for discharging processed sludge biomass, the methane synthesis device is operated at a temperature of 20° C. to 60° C., a pH of 6.5 to 8 and a redox potential of −150 mV to −450 mV
As indicated, the acidification of the biomass yields, amongst others, phase separation of the acidified biomass. Accordingly, in a preferred embodiment, phase separation of acidified liquid and sludge biomass is performed before methane synthesis by microbial conversion.
According to a further preferred embodiment, the present apparatus comprises between the methane synthesis reactor (3) and the nitrification reactor (4) a vacuum device for concentrating the processed liquid biomass, the vacuum device comprises an inlet for receiving processed liquid biomass from the methane synthesis reactor (3) and an outlet for discharging concentrated processed liquid biomass to the nitrification reactor (4), an outlet for discharging CO2 and methane and an outlet for discharging CaCO3 and NH4MgPO4, the vacuum device is operated to subject the processed liquid biomass to a vacuum of 20 to 200 mbar until a pH of at least 8, preferably at least 8.5.
By subjecting processed liquid biomass to a vacuum not only the dissolved methane is extracted, thereby increasing the yield of the present apparatus, but also dissolved CO2. By extracting CO2, the pH of the processed liquid biomass increases to the indicated range and, as a result, phosphor and magnesium in the form of NH4MgPO4 and calcium in the form of CaCO3 precipitates and, accordingly, can be conveniently removed from the process stream as a high-grade product.
NH4MgPO4 and CaCO3 removed can be brought to a substantially neutral pH, for example by using the SO4− from the effluent gas conversion reactor (5), yielding a directly marketable product.
As indicated, the present apparatus is substantially kept in homeostasis, after start-up, for the indicated process conditions by microorganisms. However, for example depending on the type of biomass supplied to the apparatus, process conditions can deviate from the indicated conditions, for example, the pH in the acidification reactor can vary depending on the nitrogen content of the biomass supplied.
Accordingly, according to a preferred embodiment, the present apparatus comprises a controlling device to monitor the indicated pHs, temperatures and/or the redox potentials, and preferably, further comprises reactors, where appropriate, provided with heating devices for maintaining the temperature in the defined range, with pH regulating devices for maintaining the pHs in the defined range, and redox potential regulating devices for maintaining the redox potential in the defined range.
Temperature regulating devices can be heaters providing heat generated or derived from the apparatus itself, or heat from an external source, coolers providing cooling generated or derived from the apparatus itself, or cooling from an external source.
pH regulating devices can be holders comprising sugar, buffer, acid or basic liquid fitted with supply means for introducing the sugar, buffer, acid or basic liquid in the appropriate reactor, and/or a transport system controlling the flow of basic or acidic fluids in the apparatus itself, for example the leachate produced by the composting reactor (6).
Redox potential regulating devices can be holders comprising liquids with a defined redox potential fitted with supply means for introducing the liquids in the appropriate reactor.
According to still another preferred embodiment, the present one or more communicating inlets and outlets of the reactors comprise devices for isolation of microorganisms and for reintroducing the isolated microorganisms in the reactors from which they were derived from.
In other words, the microorganisms in a reactor inherently discharged with the process flows are continuously reintroduced into the reactor thereby providing a stable culture of microorganisms in the reactor, and, accordingly, a stable control of methane synthesis and other microbial processes.
The present apparatus is particularly suitable to process biomass, especially to convert biomass into methane and/or fertilizer, selected from the group consisting of liquid manure, manure, sewage sludge, domestic vegetable waste, agricultural plant residue, domestic plant residue, and combinations thereof.
As indicated above, methane and other high-grade products can be conveniently collected at the outlets of reactors comprised in the present apparatus. Accordingly, according to a preferred embodiment, the present invention relates to an apparatus wherein the methane is collected at the outlets of the methane synthesis reactor (2) and the methane synthesis reactor (3) and the fertilizer at the outlets of the nitrification reactor (4) and/or the composting reactor (6).
The apparatus as described above provides an efficient conversion of (waste) biomass into valuable products. Therefore, according to another aspect, the present invention relates to a method for conversion of biomass comprising:
According to a preferred embodiment of the present method, the processed sludge biomass from the methane synthesis reactor (2) is transported to a composting reactor (6) operated at a temperature of 45° C. to 75° C., a pH and an atmospheric air concentration of 2 to 20%.
According to another preferred embodiment of the present method, acetate comprising leachate is transported from the composting reactor (6) to the acidification reactor (1).
According to still another preferred embodiment of the present method, the biomass is selected from the group consisting of liquid manure, manure, sewage sludge, domestic vegetable waste, agricultural plant residue, domestic plant residue, and combinations thereof.
According to a further preferred embodiment of the present method, the conversion of biomass comprises conversion of biomass into methane and/or fertilizer.
The apparatuses and methods as described above provide an efficient conversion of (waste) biomass into valuable products. Therefore, according to another aspect, the present invention relates to use of the present apparatuses for conversion of biomass, preferably the biomass is selected from the group consisting of liquid manure, manure, sewage sludge, domestic vegetable waste, agricultural plant residue, domestic plant residue, and combinations thereof.
According to a preferred embodiment, the present use results in the conversion of biomass into methane and/or fertilizer.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/051308 | 1/31/2011 | WO | 00 | 10/9/2013 |
