Method for separating water from end-fermented biomass

Abstract

Method for separating water from end-fermented biomass, for example from digestate from biogas processes, in which acetic acid is added to the biomass for foaming and iron sulfate for flocculation, and in which the foamed and flocculated biomass is arranged on a sieve device or is arranged for separating water to form a treated digestate.

Description

[0001] The invention relates to a process for separating water from end-fermented biomass, for example from digestate from biogas processes, in which acetic acid is added to the biomass to cause foaming and iron sulfate to cause flocculation, as well as uses of the end products obtained by the process.

[0002] Fully fermented biomass has a low dry matter content and therefore an even lower organic dry matter content. The main component of fully fermented biomass is thus water.

[0003] In some areas of Germany, only a limited amount of digestate from biogas plants may be spread on agricultural land, so there is a need for digestate processing.

[0004] Relatively labor-intensive and / or energy-intensive membrane or evaporation technologies are known for this purpose. These processes require extensive expertise, are very investment-intensive, and have high energy demands. Consequently, the processing of digestate using these methods results in high costs.

[0005] In DE 10 2013 007 829 B4, a process for treating agricultural slurry is described in which the slurry is treated with a precipitating agent in a settling and / or separation process and separated into a thick phase and a thin phase or clear phase, whereby water is additionally used as a separation agent, such that the suspended solids precipitated during the reaction of the precipitating agent with the slurry float on the separating agent water and / or sink in the separating agent water, and a thick phase thus separated can be separated from a clear phase zone by zone, wherein the supply of the slurry stream as well as the supply of the precipitating agent and the separating agent can be changed in their respective order and the supply of the precipitating agent, the separating agent and the slurry takes place in a pumped pipe or pipe section.

[0006] In addition to the above publication, DE 10 2013 017 531 B4 discloses that the separation of particles and dissolved substances in agricultural slurries or in slurries from agricultural cleaning or production plants is equally feasible if the precipitating agent iron(II) chloride or iron(III) chloride or iron(III) sulfate or iron(III) chloride sulfate is added to the precipitating agent in the form of solutions of iron(II) chloride or iron(III) chloride or iron(III) chloride sulfate in water or is added to the slurry together with water as a separation agent.

[0007] DE 10 2013 010 007 A1 relates to a process for separating a suspension, preferably from wastewater and sludge, in particular sewage sludge from sewage treatment plants, into a solid concentrate containing essentially solids and a filtrate containing essentially liquid, comprising the steps of: a) adding a starch-based flocculant to the suspension, b) separating the flocculated solid concentrate containing essentially solids from the filtrate containing essentially liquid, c) optionally drying the solid concentrate; and products produced thereafter.

[0008] DE 10 2013 003 592 A1 describes a device for separating the thick phase from the thin phase in a liquid containing suspended particles, such as agricultural slurry. To make the separation of the thick and thin phases more dynamic, avoid blockage of the flow by clogged filters, and significantly reduce the energy required for this separation, the device is designed so that the slurry is mixed with a precipitating agent before being introduced into a settling tank, or a precipitating agent is added to the slurry. Subsequently, in the settling tank, the suspended particles already present before precipitation and / or those created by precipitation settle out or are separated as the thick phase. The settled or separated thick phase is then drawn off separately from the thin phase that forms the clear zone.

[0009] DE 10 2014 005 065 A1 relates to a process for treating agricultural slurry by treating the slurry with a precipitating agent in a settling and / or separation process and separating it into a thick phase on the one hand and a thin phase or clear phase on the other, as well as to an apparatus for carrying out the process. To ensure that precipitation is optimized even with heavy slurries, requiring minimal amounts of precipitating agent while maintaining optimal precipitation, water is additionally enriched with at least some hypochlorous acid and used as a separation agent. The suspended solids that precipitate during the reaction of the precipitating agent and the hypochlorous acid with the slurry float on the surface of the water and / or sink within it, allowing a thick phase to be separated from a clear phase in zones.

[0010] The invention is based on the objective of providing a method for separating water from fully fermented biomass, for example from digestate from biogas processes, which is simple and cost-effective to implement.

[0011] This problem is solved by the method specified in claim 1. In the inventive method for separating water from fully fermented biomass, for example, digestate from biogas processes, acetic acid is added to the biomass to cause foaming, and ferrous sulfate is added to cause flocculation. The foamed and flocculated biomass is or is arranged on a sieve device to separate the water and form a treated digestate.

[0012] Using the process according to the invention, water can be separated from the fully fermented biomass in a technically simple manner.

[0013] Another advantage of the method according to the invention is that it requires only extremely little equipment and is therefore easy and inexpensive to carry out.

[0014] The addition of iron sulfate causes a structural change in the biomass.

[0015] In a further development of the process according to the invention, the acetic acid and the iron sulfate are added simultaneously to the biomass to be treated.

[0016] Depending on the specific requirements and process conditions, the acetic acid and the iron sulfate can also be added at different times.

[0017] The basic principle here is that an acid is added to cause foaming. To induce a structural change in the form of flocculation, a flocculant is used. In this context, acetic acid is used as the acid and ferrous sulfate as the flocculant.

[0018] Another embodiment of the process according to the invention provides that the treated digestate is mechanically pressed to further separate water and form a final product. In this embodiment, water is first separated from the biomass by foaming in a first stage of the process. In a second stage of the process, further water is then separated by mechanical pressing.

[0019] A further development of the aforementioned embodiment involves final drying of the final product. This further reduces the water content of the final product.

[0020] In order to make the process particularly energy-efficient in the aforementioned embodiment, an advantageous further development of this embodiment provides that waste heat is used for the final drying of the end product.

[0021] In the aforementioned embodiments, the finally dried product can be used as biological fertilizer or as fuel.

[0022] Another advantageous embodiment of the invention provides that the final product is pyrolyzed.

[0023] The invention is explained in more detail below using a method example. Example procedure:

[0024] In one embodiment of the process according to the invention, acetic acid, as a substance that causes the biomass to foam, and ferrous sulfate, as a substance that causes a structural change in the biomass, are added to the fully fermented biomass. According to the invention, the biomass is arranged on a sieve or filter with a not-too-fine mesh, whereby water, in an amount of approximately 65 percent to 75 percent of the original mass of the fully fermented biomass, spontaneously and in a relatively short time passes through the sieve / filter.

[0025] In a second stage of this embodiment of the process according to the invention, the fermentation residue undergoes a structural change through foaming, such that it is now compressible and releases even more water through mechanical treatment. Mechanical treatment offers the advantage of higher energy efficiency compared to thermal treatment.

[0026] As an alternative to mechanical treatment, the remaining solid residue can be stored on a sieve base for a longer period of time so that further water can drain off.

[0027] In a third stage of this embodiment of the process according to the invention, the resulting substance can be dried, particularly by utilizing waste heat. The resulting end product is a biological fertilizer and can be packaged and sold.

[0028] If the fully fermented biomass is contaminated, it can also be dried, particularly by utilizing waste heat. The resulting end product can then be sold as fuel to coal-fired or biomass (heating) power plants. It can also be used as fuel for wood-burning stoves in briquette form.

[0029] In a fourth stage of this embodiment of the process according to the invention, the finally dried end product can be pyrolyzed. This yields three fractions, namely pyrolysis coke, pyrolysis oil, and pyrolysis gases, all of which can be advantageously used further.

[0030] The solid residue remaining after pyrolysis is called pyrolysis coke. In the first stage of the process according to the invention, the pyrolysis coke can be used to filter the water that emerges and contains the phosphate present in the fermented biomass. Its use as a filter also results in the binding of nitrate. When applied to and incorporated into arable land, the pyrolysis coke acts as a fertilizer. Furthermore, due to its stable matrix, it binds carbon in the soil, contributing to the reduction of free carbon and thus to the reduction of carbon dioxide (a greenhouse gas) in the atmosphere. In addition, it loosens the soil structure, which is another positive effect.

[0031] The condensed liquid fraction is called pyrolysis oil. It is a mixture of various hydrocarbons. Pyrolysis oil can be used as fuel. Alternatively, it can be sold to the petrochemical industry for use as an additive for crude oil reduction in refining or steam cracking.

[0032] The non-condensing portion is called pyrolysis gas. This is also a mixture of hydrocarbons. Pyrolysis gas can be used directly as fuel for combined heat and power plants or for other types of combustion engines.

[0033] In the aforementioned process example, stages 1 to 3 should take place at the site where the fermented biomass is produced. Due to the required plant size, stage 4 should be carried out centrally for several locations of the preceding process stages. Dewatering and drying mean that only a fraction of the original mass needs to be transported, which reduces both transport costs and the necessary energy (fuel) consumption.

Claims

[1] Method for separating water from end-fermented biomass, for example digestate from biogas processes, in which acetic acid is added to the biomass to foam it and ferrous sulfate to flocculate it, and in which the foamed and flocculated biomass is arranged on a sieve device to separate water, forming a treated digestate. [2] Method according to claim 1, wherein the acetic acid and the ferrous sulfate are added to the biomass to be treated simultaneously. [3] Method according to claim 1 or 2, wherein the treated fermentation residue is mechanically pressed to further separate water in order to form a final product. [4] Method according to claim 1 or 2, wherein the treated digestate is stored on a sieve substrate for a longer period of time to further separate water from the digestate and to form a final product. [5] Method according to claim 3 or 4, wherein the final product is dried. [6] Method according to claim 5, wherein waste heat is used for the final drying of the final product. [7] The method of claim 5 or 6, wherein the final product is pyrolyzed. [8] Use of the final dried end product produced according to claim 5 or 6 as a biological fertilizer. [9] Use of the final dried end product produced according to claim 5 or 6 as fuel.