EP2598602A1

EP2598602A1 - Soil conditioner, system and method for the manufacturing of a soil conditioner

Info

Publication number: EP2598602A1
Application number: EP11745587.3A
Authority: EP
Inventors: Philip John Risby; Ove Lerdahl
Original assignee: Agroplas AS
Current assignee: Agroplas AS
Priority date: 2010-07-26
Filing date: 2011-07-26
Publication date: 2013-06-05
Also published as: WO2012015313A1

Abstract

The present invention concerns a system for the manufacturing of a soil conditioner, a method for the production of the soil conditioner, and the soil conditioner produced by said method.

Description

Soil conditioner, system and method for the manufacturing of a soil conditioner Field of invention

The present invention concerns a method for the production of a soil conditioner, a system for the manufacturing of the soil conditioner, and the soil conditioner produced by said method.

Background of invention

In agriculture methane may be regarded as a problem. The main component of biogas generated in fermentation of organic matter under anaerobic conditions is methane. Organic matter fermented could be manure, domestic waste in landfills, and sludge from waste water purification. The gas constitutes a local problem when generated in manure pits or liquid-manure tanks as it is highly flammable. In mixture with air methane may also form an explosive mixture.

In a closed space methane may displace oxygen and result in asphyxia when oxygen concentration is reduced below a critical level. Since methane is both colorless and odorless there is no warning of its presence. People and livestock have died from suffocation due to methane leakage into outbuilding from manure tanks.

Flammable or explosive mixtures are formed at concentrations of methane that are much lower than the concentrations at which asphyxia is a significant risk. Methane is also a potent greenhouse gas and with a global warming potential that far exceeds that of carbon dioxide.

On the other hand methane is an energy source which may be used to produce for instance electricity and heat. However due to the fairly small amounts of methane produced at each site from fermentation of waste (e.g. manure, landfill, domestic waste and sludge), the methane has generally been burned off to avoid hazardous explosive mixtures.

The use of carbon as soil conditioner has a long history from the burning off of withered grass and leaves, through spreading of collected black carbon and soot to improve the soil quality. US 2010/0004126 Al discloses a soil conditioner containing a carbonized substance which has a percent carbonization of at least 90 %. The carbonized substance has a porous, amorphous structure including numerous pores and has substantially no hydroxyl groups. The pores contain micropores having a pore size of 0.1 μηι or less in an amount of at least 25 %, and the micropores are in communication with one another. The soil conditioner is employed in the form of powder or particles.

In JP4280811 Al improvement of the soil of golf course etc. is disclosed. Bamboo powder is heated at 400 to 600 °C to produce activated carbon. The thus produced activated carbon is applied to improve the soil of e.g. golf courses. Air penetration, water permeability properties, water retaining properties and fertilizer retaining of the soil can be improved.

JP9310068 concerns a soil conditioner comprising carbon material composed of combustion residues of waste rubber products with the following characteristics: i) pore size: 0.005 - 0.1 μπι, n) specific surface area: 30 - 500 m /g, and iii) porosity: 1.0 - 5.0 ml/g.

Carbon sources of unknown composition i.e. carbon containing waste material are potentially hazardous as they may contain components that are environmentally harmful or toxic. Also the preparation of activated carbon through combustion of carbon containing waste material may be environmentally disadvantageous as the waste gas from the combustion can contain harmful components.

Environment protective regulations require that soil additives e.g. soil conditioners are safe and do not add pollutive agents to the soil.

Ordinary fertilizers contain nitrogen (e.g. ammonia, urea, and nitrate, "N"), phosphorus ("P") and potassium ("K") but not carbon, and some soils will eventually suffer from carbon depletion which will affect the crop. The present invention provides a scalable system and a method where soil conditioner/fertilizer may be produced locally on demand from sources otherwise regarded as waste.

Ammonia is an important nitrogen source in fertilizers. Even if nitrogen is the most abundant gas in the earth's atmosphere it is not accessible to plants. Industrially ammonia may be synthesized by the so called Haber-process wherein nitrogen and hydrogen is reacted to ammonia in the presence of a metal oxide catalyst, under high pressure (15-25 MPa) and a temperature of 300-550 °C.

The hydrogen used in this process is normally produced from methane or natural gas through a multi step, energy consuming, heterogeneous catalytic process known as the Haber-Bosch process. Ammonia is further converted to nitric acid to produce synthetic fertilizers.

The processes involved in production of synthetic fertilizers are complex, energy consuming and also involve steps that are potentially hazardous. These and other factors require a central production of fertilizers, where the final product is distributed to farmers. The central production of fertilizers involves transportation of raw materials to the central production site and then distribution to the individual farmers often through several retail steps.

The digestate remaining after anaerobic fermentation of organic waste to produce biogas (i.e. methane) is a slurry containing valuable nutrients. However the nutrients in the slurry are so diluted in water that it is no practical and economical viable way to use this source of plant nutrients. Many farmers thus experience a need for an easy and practical way to access this nutrient source locally without violating restrictions concerning leakage to ground water, rivers etc. as when manure is spread directly as natural fertilizer. Another issue in that respect is the problem with bacterial contamination of the crop, particularly vegetables and the like for human consumption.

The present invention provides a method and a system which is easy scaleable for use both in an industrial scale and at the individual farm. The system can be produced inexpensively and thus become economically viable also in small scale facilities.

Brief description of the drawings

Figure 1 shows a schematic illustration of one embodiment of the present invention.

Figure 2 is a schematic illustration of a second embodiment of the present invention. Figure 3 is a schematic illustration of a Vortair mixing and drying apparatus. Summary of invention

The present invention provides a system for the manufacturing of a soil conditioner wherein a gaseous hydrocarbon source is fed to plasma cracking unit (5), and the produced carbon (6) is fed to a unit (4) wherein the carbon is mixed with a substrate (1), and optionally the substrate is dried before mixing in the mixing unit (4) or in a separate dryer to produce a soil conditioner comprising carbon.

A method for the production of a soil conditioner wherein a gaseous hydrocarbon source is plasma cracked, and the carbon produced is mixed with a substrate and the substrate is optionally dried before the mixing or the mixing and drying is performed simultaneously is also provided by the present invention.

Further a soil conditioner is provided which is produced by the method of the present invention.

Detailed description

The following terms shall herein have the meanings as indicated below unless otherwise specifically stated:

Bio-methane - methane produced from anaerobic fermentation of organic waste.

Digestate - is the material remaining after the anaerobic digestion of a

biodegradable feedstock such as organic waste. Methanogenic digestate is a sludge or slurry with high water content.

Natural gas - the general meaning i.e. gas mainly consisting of methane found associated with fossil fuel.

Stranded gas - natural gas otherwise burned off as waste. Organic waste includes manure, landfill, household waste, sludge from water purification, agricultural and forestry waste, crop waste. Plasma carbon - elemental carbon produced by plasma cracking of gaseous hydrocarbons.

When methane is produced by anaerobic fermentation of organic waste, the digestate from this production holds components valuable as fertilizers. Methane from fermented organic waste or natural gas is through plasma cracking converted into elemental carbon (activated carbon, carbon black) and hydrogen gas (H₂).

Stranded gas i.e. natural gas that otherwise is burned off without taking advantages of the energy it produces. Natural gas, mainly methane, is a more potent green house gas than carbon dioxide resulting from the burn off.

When methane from fermented organic waste is used as carbon source the soil conditioner of the present invention will be carbon-negative i.e. carbon will be stored in the soil instead of being emitted to air. Even when natural gas is used as the carbon source the soil conditioner will be carbon-neutral. Plasma cracking may be performed by any known method in the art producing elemental carbon and hydrogen gas. It is however preferred to perform the plasma cracking in a reactor for microwave-generated plasma. Particularly the latter is preferred for gaseous hydrocarbons in smaller installations.

Plasma carbon form microporous particles with extremely large surface in the area 50 m /g to 1000 m /g. The structure of the plasma carbon is important for the characteristics of the soil conditioner according to the invention. The porous plasma carbon can improve retention of water and nutrients in the soil. Further, toxic components are adsorbed by the carbon particles and thus neutralized. Adsorbed heavy metals are kept in the carbon structure and are thus made less harmful. The carbon particles' ability to retain water, nutrients, and adsorb toxic compounds and heavy metals is important as leakage of these components into ground water, streams and rivers can be reduced significantly.

Biochar and organic matter carbonized, for instance by pyrolysis, comprise organic/aromatic carbon structures which will be gradually decomposed by bacteria in certain soils producing carbon dioxide. The plasma carbon contains no aromatic structures and is thus more inert and less exposed to bacterial decomposition. It is likely to provide a millenial carbon sink when introduced into soils.

Plasma carbon with small nodule sizes (<100nm) has several advantages as soil conditioner since it absorbs UV radiation and thus provides protection for microorganisms which are vital for the good growth conditions in soils that are exposed to strong solar radiation. Additionally the plasma carbon, by improving the soil structure, has water retention properties and can thus prevent dehydration of the soil.

The by-product, H₂, has several applications in industry and as an energy carrier for fuel cells. Petroleum industry requires large quantities of H₂ in the processing of fossil fuels, and chemical industry needs ¾ as a hydrogenating agent and as a reducing agent, as well as for the production of ammonia,

Several other applications of hydrogen can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries, particularly as feedstock for fuel cells.

Hydrogen gas may also be used in the production of biofuels wherein carbon dioxide and hydrogen gas are converted into methanol. Methanol is an liquid energy carrier at atmospheric pressure and room temperature which provides easier handling than hydrogen gas. Hydrogen can also be used as a fuel for local heating, with only water vapour as the product of combustion.

The present invention provides a system for the manufacturing of a soil conditioner wherein carbon from plasma cracking of methane or natural gas is added to a substrate in a mixing unit. Optionally the substrate may be dried before mixing with the carbon or the drying may be performed simultaneously with the mixing in a combined drying-mixing unit.

In one embodiment of the invention the system comprises a reactor for anaerobic fermentation (1) of organic waste, bio-methane produced in the reactor may be treated to remove water vapour and other contaminants and thereafter is transferred to a plasma cracking reactor (5) through suitable means (3) like a pipeline.

Substrate, e.g. digestate from the fermentation, optionally decanted, is transferred by suitable means (2) to a combined drying and mixing apparatus (4). Water from the drying is evaporated or drained off (11) from the drying/mixing apparatus (4). Plasma carbon is transferred by suitable means (6) to the drying/mixing apparatus (4) where it is mixed with the substrate and coated on said substrate. The mixed and dried product is transferred from the mixing/drying apparatus trough an out let (7) and collected in suitable container (8). Hydrogen gas produced in the plasma cracking reactor is led from an out let of the plasma reactor (5) trough a pipeline (7) to a container (10) suitable for combustion or storage of said hydrogen gas.

Another embodiment of the system comprises separate drying and mixing units, wherein the substrate is dried in before it is transferred to the mixing unit. The carbon is introduced to the mixing unit and substrate and carbon are mixed to form the soil conditioner product which is transferred from the mixing apparatus to a storage container (8) by suitable means (7).

In a further embodiment of the system natural gas (12) is introduced to a plasma cracking reactor (5) through suitable means (3), and the produced plasma carbon is mixed with and coated on a substrate such as sand in a mixing apparatus (4) The present invention also provides a method for the production of a soil conditioner wherein a substrate (1) may be is dried and then mixed with carbon produced by plasma cracking of methane or natural gas. The carbon is mixed with the substrate and coated on the surface of substrate particles. The resulting product is well suited as a soil conditioner with several advantageous characteristics.

Hydrogen gas produced in the plasma cracking is collected.

In another embodiment of the method according to the invention plasma carbon is mixed into organic waste subject to anaerobic fermentation to improve the fermentation process and also improve the retention of nitrogen by adsorption to the carbon. In organic waste nitrogen often exists as ammonia/ammonium which otherwise is washed out causing overfertilisation.

According to yet another embodiment of the invention a soil conditioner is provided which is produced by the method according to the invention.

The drying and mixing may be performed in any apparatus capable of performing the operations simultaneously, such as a flash or ring dryer, a Vortair, or similar equipment. A ring dryer is a development of the flash dryer and is the market leading drying system for agricultural wastes and sludge. It uses heated air as the drying medium and incorporates a hammer mill within the circuit for grinding the product together with an air classifier for control of particle size. It frequently incorporates blending means within the system that would enable the mixing of carbon with the material to be dried.

The Vortair Processor is a low-energy drying and grinding system illustrated in figure 3. Carbon (1 12) and substrate (1 1 1) are supplied to the Vortair (1 10) and carried round the drying chamber by a highly turbulent stream of drying air. During drying water (1 13) is evaporated and leaves the system with the drying air. The product i.e. the soil conditioner (1 14) is collected and stored for spreading or packaging for distribution.

In both the ring dryer and the Vortair drying and mixing may be performed in the same apparatus unit. The invention is however not limited to such combined apparatuses since the drying of the substrate may be performed by any means known in the art. The mixing of dry substrate and plasma carbon may be performed by any means for mixing known in the art.

The substrate to be mixed with carbon is selected from the group consisting of different soil types, e.g. sand, clay, silt and loam digestate from organic waste fermentation, sludge from water treatment facilities, or indeed any other material known to be beneficial to agriculture.

When the substrate is digestate from organic waste fermentation the product is a combined soil conditioner and fertilizer.

Claims

A system for the manufacturing of a soil conditioner wherein a gaseous hydrocarbon source is fed to plasma cracking unit (5), and the produced carbon (6) is fed to a unit (4) wherein the plasma carbon is mixed with a substrate (1), to produce a carbon enriched soil conditioner.

System according to claim 1 wherein the gaseous carbon source is bio- methane or natural gas.

System according to any one of claims 1 to 2 wherein the substrate is selected from the group consisting of soil, digestate from organic waste fermentation, sludge from water treatment

System according to any one of claims 1 to 3 wherein the substrate (1) is coated with carbon in the mixing unit (4).

System according to any one of the preceding claims wherein the mixing unit is a circular vortex air flow material grinder.

A method for the manufacturing of a soil conditioner wherein a gaseous hydrocarbon source is plasma cracked, and the carbon produced is mixed with a substrate and the mixture is ground and optionally dried where the mixing, grinding and drying is performed simultaneously.

Method according to claim 6 wherein the mixing and drying step is performed in a circular vortex air flow material grinder.

Method according to any one of the preceding claims 6 to 7 wherein the substrate is selected from the group consisting of soil, sand, digestate from organic waste fermentation or sludge from water treatment.

Method according to any one of claims 6 to 8 wherein plasma carbon is fed to the organic waste being fermented.

A soil conditioner produced by the method according to any one of claims 6 to 9.