DK171735B1 - Use of lime soaps and / or magnesium soaps in biogas production and method of biogas production - Google Patents

Description

DK 171735 B1

The present invention relates to the use of lime soaps and / or magnesium soaps in biogas production as well as to a method of biogas production.

In many cases, biogas production is based mainly or solely on livestock manure and urine, so-called manure, or on raw sludge or active sludge from wastewater treatment plants. However, many other wastes can be included in the substrate fermented in a biogas reactor, partly as a useful measure to get rid of such wastes, and partly to serve as an energy supplement and thus increase the yield of biogas which, as is known, consists predominantly of methane. .

It is an obvious thought to use waste grease as such an additional fermentation substrate. However, it causes a number of problems that it has hitherto considered difficult to solve.

Sludge used in biogas reactors has a water content of about 85-95% and is thus quite liquid as slurry is most frequent. When fat is added, such as triglycerides, it can rise upward in the reactor and be trapped in flow layers.

During fermentation, the fat will first be hydrolyzed to free fatty acids and glycerol, and the free fatty acids form at pH about 7 - which is normal in biogas reactors - ammonium soaps due to the nitrogenous compounds in the slurry and sludge. The ammonium soaps can cause severe foaming problems at the gas exit.

In addition, the fat addition in itself can give a strong gas evolution which can lead to operational disturbances in combination with even weak foaming.

Finally, impurities of ammonium soaps and optionally alkali metal soaps can settle around the microorganisms and / or fermentation material particles, thereby dampening the fermentation change.

35 2 DK 171735 B1

European Patent Specification No. 114,769 discloses a process for the production of methane by anaerobic fermentation of organic substrates under otherwise normal conditions, wherein the fermentation medium contains a small amount of -5 0.001-0.35 mM / 1 - of an unsaturated fatty acid. (or esters thereof) containing 18-22 carbon atoms and at least two olefinic double bonds. It is shown in the document that the gas yield is thereby substantially increased. Thus, these fatty acids act as activators, but do not contribute significantly to the energy supply. It is believed that adding substantially larger amounts of these fatty acids will cause the aforementioned disadvantages. Moreover, it appears from the introduction of the script that the fatty acids mentioned since 1967 have been known as inhibitors of methane production.

15 According to European Patent No. 159,972 it is stated that resin acids and higher fatty acids and sodium salts thereof are toxic to methane bacteria in the anaerobic treatment of wastewater, and that addition of iron salts and / or aluminum salts only has no effect on the toxicity and that the toxicity is only affected. to a small extent by the addition of calcium salts alone and / or magnesium salts. In contrast, toxicity is abolished by the addition of both iron and / or aluminum salts and partly calcium and / or magnesium salts.

Against this background, it is surprising that one can solve or at least substantially limit the problems described above by using a mixture containing lime soaps and / or magnesium soaps as an energy supplement in biogas production.

The process according to the invention is of the kind in which a biogas reactor produces biogas using fatty acid-containing material as part of the energy source, and the process according to the invention is characterized in that in the supply of energy-containing material 35 to the biogas reactor a mixture containing lime soaps is included. / or magnesium soaps.

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By lime and magnesium soaps, in this specification, claims refer to not only Ca and Mg salts of fatty acids, but generally Ca and Mg salts of lipids, by which the term refers to substances which in accordance with the definition of The Condensed Chemical Directionary, 8th Edition, Van Nostrand Reinhold Co., New York 1971, are substances that are (i) relatively insoluble in water but soluble in fat solvents such as benzene, chloroform, acetone and ether, (ii) actual or potentially 10 are related to fatty acid esters and (iii) usable in animal organisms. In addition to mono-, di- and triglycerides, the term lipids is thus used, among other things, to to free fatty acids and phospholipids such as lecithins.

At the pH value of about 15 7 in the biogas reactor, the typical lime soap, ie calcium salts of fatty acids, slowly decomposes to fatty acids and calcium, while other lipid salts undergo analogous reactions. The fatty acids are broken down by fermentation to methane and carbon dioxide, while calcium is precipitated as CaCO 2. Analogous conditions apply to magnesium soaps here as in the following parts of the specification, which therefore essentially explain the invention as the use of lime soaps.

When the fatty acids are added in the form of lime soaps, the equilibrium concentration of fatty acids in the sludge under 25 fermentation (decay) is kept so low due to the slow decomposition of the lime soaps that there is no risk of significant formation of ammonium soaps and therefore, no stormy reaction with heavy foaming that could cause clogging of pipelines in the reactor, including its effluent for biogas generated.

The lime soaps can be added as such, resulting from various industrial sources of grease in the form of lime soaps, for example from the food industry and the pharmaceutical industry.

However, other sources of waste grease can also be used as a lime-soap source, since before it is introduced into the biogas reactor it is reacted with finely divided lime (eg in the form of burnt lime or slaked lime (CafOH 2)); roasted lime is the cheapest source of calcium and at the same time has the advantage of developing heat in the curing process that the lime undergoes by lime treatment of the 5 fat in aqueous phase.

In lime soap production with burnt lime or slaked lime, virtually all mono-, di- and triglycerides are saponified and free glycerol is obtained. Therefore, as a lime soap source, the whole of the glycerol-containing reaction product obtained by Ca and / or Mg saponification can be used as an energy supplement in biogas production, since glycerol is an excellent substrate for the bacteria active in biogas reactors.

In particular, according to the invention, the glycerol-containing mixture obtained as an energy supplement in biogas production can be used in 15 Ca and / or Mg saponification of waste material or waste material containing fats.

In addition, the glycerol content promotes the calcium soap slurry in the biogas reactor. The effect may be due to the fact that glycerol acts as a moisturizing agent or that the glycerol is mixed into the lime soap mass in such a way that this mass falls apart into very fine particles when the glycerol is dissolved in a larger volume of water.

Lime soap made from glycerides is slurried and moistened much more easily than lime soap made from pure fatty acids.

Saponification of triglycerides with CafOH as a base, frequently added in the form of CaO or calcareous materials, optionally waste materials, takes place vigorously at 85-90 ° C under high positive heat toning. Therefore, it is possible to use materials with relatively low content of calcium oxide or calcium hydroxide.

Fat sources may often have a significant portion of the fatty acid content, e.g., 30-60%, in the form of free fatty acids. This is the case, for example, of foamed fat from the fat trapped in purification plants, since the biological activity has often been high during transport and the biodegradation of fats starts with hydrolysis of the ester bonds.

Free fatty acids are currently precipitated as lime soap by mixing with Ca (OH) 2 ~ containing media.

In the saponification of fatty acids and especially fatty acid glycerides, it has been found appropriate to use molar amounts of calcium and fatty acid (s).

Two advantages are thus obtained by using about twice the stoichiometric amount of calcium (magnesium): 10 First, the saponification reaction proceeds more rapidly and to a greater extent than otherwise. This is probably because the base effect of Ca (OH) 2 is much higher than the base effect of Ca (OH, fatty acid residue). The pH of the latter product is in aqueous slurry 8-9, but the pH of Ca (OH) 2 is 11-12. In addition, Ca (OH, fatty acid residue) is not soluble in water, and this is perhaps the main reason why this substance does not appear to participate in the further saponification of fatty acid glycerides in aqueous medium.

Second, Ca (OH, fatty acid residue) is suspended as very fine particles in bioreactor sludge, possibly due to reaction with bicarbonate or carbonic acid, possibly due to some polar nature of the substance.

Examples of sources of waste grease that can be saponified for use in biogas reactors can be grease scrap from wastewater treatment plants, grease from grease traps in the food industry and tank wastewater sludge as well as many wastewater treatment plants. Greasy sludge from tank cleaning in companies that manufacture or process animal, vegetable and marine oils often contains a substantial 30 excess lecithins. When treated with lime or cured lime, the lecithins are cleaved so that both fatty acids and phosphorus are precipitated with calcium. Analogously, cholesterol-containing waste fat by treatment with lime or slaked lime can be brought into a form where it can be utilized by the bacteria.

Accordingly, according to the invention, calcium salts of waste fats can conveniently be used as part of the fermentation material in reactors for the production of biogas from organic wastes.

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Magnesium salts of fatty acids are just as useful as calcium salts and other heavily soluble fatty acid salts for fermentation in rot tanks, including biogas reactors.

Basic magnesium compounds are not 5 in most countries. as readily available as basic calcium compounds. But in some countries, burnt dolanite (dolomite is a magnesium-calcium carbonate) is used instead of burnt lime, and in that case it can be an appropriate source of calcium-magnesium soap.

The invention will now be further illustrated by an exemplary embodiment.

Example 3 - In a biogas reactor with a capacity of 450 m, which was in stable operation with slurry as the substrate for the fermentation, 250 kg of lime soap with a fatty acid content of 85 wt.

3 In the reactor, 400 m of biogas was developed over 4 days in addition to the normal production of 200 m 2 of biogas per day for the reactor.

There was no suggestion of increased foaming, change of pH or other types of operational disturbance.

25 30 35.

Claims (5)

1. Use of lime soaps and / or magnesium soaps as energy supplement in biogas production. Use according to claim 1 of calcium salts and / or 5 magnesium salts of waste fats as part of the fermentation material in reactors for producing biogas from organic wastes. THAW Use according to claim 1 of the glycerol-containing reaction product obtained by Ca- and / or Mg-fat saponification as an energy supplement in biogas production. Use according to claim 2 or 3 of the glycerol-containing mixture obtained as energy supplement in biogas production by Ca and and / or Mg saponification of waste fats or waste material containing fat. Process of producing biogas in a biogas reactor using fatty acid-containing material 20 as part of the energy source, characterized in that a mixture containing lime soaps and / or magnesium soaps is included in the supply of energy-containing material to the biogas reactor.