NZ225414A

NZ225414A - A process for the production of biogas characterised in using calcium and/or magnesium soaps; biogas

Info

Publication number: NZ225414A
Application number: NZ225414A
Authority: NZ
Inventors: Niels Lang Mathiesen
Original assignee: Niels Lang Mathiesen
Priority date: 1987-07-14
Filing date: 1988-07-14
Publication date: 1990-11-27
Also published as: DK365387D0; DK365387A; WO1989000548A1; DK171735B1

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number £25414 NO DRAWINGS Priority Oatefs^: ... .. Complete Specification Filad: U+tT?I Class: Publication Date: ... 2.7.NJQY.J9M P.O. Journal, No: . .®, No.: Date: NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION 5414 A METHOD IN THE PRODUCTION OP BIOGAS I/j3> NIELS LANG MATHIESEN, a Danish citizen of, 9A Alfred Christensens Vej, 2850 Naerum, Denmark hereby declare the invention for which I / Pray that a patent maar^ • be granted to me/a®, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by page 1A) 225414 1ft A Method in the Production of Biogas Field and Background of the Invention The present invention relates to a method in the production of biogas. In many cases the biogas production is mainly or exclusively based on manure and urine from domestic animals, the socalled liquid manure, or on raw sludge or activated sludge from sewage treatment works. However, many other waste products may form part of the substrate under fermentation in a biogas reactor, in part as a useful measure to get rid of such waste products, in part to serve as energy supplement and hence increase the yield of biogas which, as is known, predominantly consists of methane. It is an obvious thought to use waste oils and fats as such a supplementing fermentation substrate. However, that entails a series of problems which it has been hitherto considered difficult to solve. Sludge used in biogas reactors has a water content of about 85-95% and hence is rather fluid, and so is liquid manure most frequently. When fat is added, e.g. triglycerides, it may rise in the reactor and be caught in floating layers. During the fermentation process the fat will first become hydrolyzed into free fatty acids and glycerol and at pH about 7 - which is normal in biogas reactors - the free fatty acids will form ammonium soaps because of the nitrogenous compounds in the liquid manure and sludge. The ammonium soaps may cause serious foaming problems in-' o^- //\ the gas discharge. //J" The addition of fat moreover in itself may causef^ strong generation of gas which may result in disturbaricSe^\ ^ of the operation even by weak foaming. Finally films of ammonium soaps and possibly alkali metal soaps may form round about the microorganisms and/ or particles of fermentable material and thereby hamper o 225 4 1 2 the fermentative metabolism. It has now been surprisingly found that these problems can be solved or at least substantially limited f**) when according to the invention one uses the oils and 5 fats in the form of calcium soaps and/or magnesium soaps as energy supplement in the production of biogas. For the removal of nitrate from water, i.e. for the purification of notably drinking water, it is known from O DE 3,440,619 with a view to bacterial nitrate reduction 10 to add natural oil or natural fat as a source of energy for the bacteria, together with a carrier substance of fine-grained alkaline earth minerals. As oil or fat there is preferably used edible oil or fat and the carrier substance, e.g. calcium or magnesium carbonate, limestone or 15 dolomite, causes at least a partial conversion of the oil or fat to alkaline earth metal soap. The purpose of using a natural fatty substance is to avoid a high concentration of organic substances, precarious from a health point of view, which is stated to be possible by an addition for 20 the same purpose of biologically decomposable compounds such as hydrocarbons, cellulose, gelatin, starch or alcohols together with solid carrier substances such as sand, gravel or particles of polyurethane foam, known from European patent Publication No. 102,584. 25 The present invention cannot be deduced from the prior art thus known; the only common feature is that some material containing fatty acid residues is used as energy source for bacteria; the bacteria active in biogas production moreover must be supposed to be others than 30 those active in nitrate reduction. The abovementioned problems of foaming in the biogas reactor by the addition of fats are not present in connection with the purifica-tion of water for use; and it goes without saying that //Q. one cannot use waste soaps or waste fats for the removal!}^ %-j. A 4 35 of nitrate from water for public use, notably drinking ^ \ 1 water. In principle the energy liberated from the oil or fat by the technique known from DE 3,440,619 is fully utilized by the nitrate reducing bacteria whereas in the ■fVJt-* -i!x I t o 3 225414 present method it is exactly intended to utilize it as biogas. O Detailed Explanation of the Invention By calcium and magnesium soaps there is meant in the present specification with claims not only Ca and Mg salts of fatty acids but generally Ca and Mg salts of lipids. By lipids there is meant in accordance with 10 the difinition in The Condensed Chemical Dictionary, Eigth Edition, Van Nostrand Reinhold Co., New York 1971, substances which are (i) relatively insoluble in water but soluble in the fat solvents (benzene, chloroform, acetone, ether), (ii) related either actually or 15 potentially to fatty acid esters, and (iii) utilizable by animal organisms. Besides mono-, di- and triglycerides thus with the word lipids there is aimed at, i.a., free fatty acids and phospholipids such as lecithins. At the pH of about 7 prevailing in the biogas re-20 actor the typical calcium soaps, i.e. calcium salts of fatty acids, are slowly decomposed to fatty acids and calcium whereas other lipid salts undergo analogous reactions. The fatty acids during the fermentation are decomposed to methane and carbon dioxide whereas calcium 25 is precipitated as CaCO^. Analogous circumstances apply to magnesium for which reason the description will mainly explain the invention as use of calcium soaps or alkaline earth metal soaps in general. When the fatty acids have been added in the form of 30 calcium soaps, the equilibrium concentration of fatty acids in the fermenting (decaying) sludge is constantly so low, because of the slow decomposition, that no ap- ___ preciable risk of forming ammonium soaps occur and cons#^T ^X vV s\ quently there will be no violent reaction with vigorous o\\ jI rr. 35 foaming which might cause clogging of conduits in the-i ). 4 a K\)bh reactor, including its discharge lines for biogas formed*. <-'/ The alkaline earth metal soaps may be - added as such; various -.-'" ■ industrial sources provide residual grease in the form O o © 225414 of such soaps, e.g. the food industry and the drug industry. It is, however, also possible to use other sources n of waste fats whereby before being introduced into the 5 biogas reactor they are reacted with comminuted lime (CaO), e.g. in the form of burnt lime or slaked lime (CafOH^); burnt lime is the cheapest calcium source and at the same time has the advantage that heat is evolved in the slaking process to which the lime is sub-10 jected during the lime treatment of the fat in the aqueous phase. In the preparation of calcium soaps with burnt or slaked lime, the free fatty acids and a high proportion of the mono-, di- and triglycerides are saponified 15 and free glycerol is formed. As source of alkaline earth metal soap one may therefore according to the invention use the entire glycerol-containing reaction product obtained by the saponification of fats with Ca and/or Mg as energy supplement in the production of 20 biogas; this is because glycerol is an excellent substrate for the bacteria which are active in biogas reactors . O Especially one may according to the invention use the glycerol-containing mixture obtained by the saponi-25 fication with Ca and/or Mg of waste products and waste material containing oils and fats as energy supplement in the production of biogas. ■f^) The glycerol content also has a promoting effect on V j suspending the alkaline earth metal soaps in the biogas reactor 30 The effect may either be due to an action of glycerol as a humidifying substance, or due to an intermixing of the glycerol into the soap mass in a manner so as to cause this mass to fall apart in very fine par->;'iA~T~q //\ tides when the glycerol is dissolved in a larger amoiar^t >W / a. o 35 of water. !j . ft- Calcium soap prepared from glycerides is suspended^^ ^ and moistened far easier than calcium soap prepared N ^ r{' ' - - - C: ' from pure fatty acids. 225414 The saponification of fatty acids and esters of fatty acids and glycerol may be carried out with cal-cium-containing basic fats, e.g. in the form of lime-precipitated wastewater sludge from purification plants for process water using calcium hydroxide as precipitation agent. Such lime-precipitated sludge products often contain organic substances which may be reacted in the biogas reactor. A considerable proportion of the fatty acids content of the fat source, e.g. 30-60%, may be present in the form of free fatty acids. This, for instance, is the case with fat skimmed off the fat trap in sewage treatment works, since the biological activity has often been high during transport and the biological decomposition of oils and fats begins with hydrolysis of the ester bonds. Free fatty acids are precipitated immediately as calcium soap when mixed with Ca(OH)2~containing media. It will often be advantageous to add lime to the fat trap sludge at the site of origin since the dehydration of lime-treated fat trap sludge is much easier than the dehydration of such sludge which has not been treated with lime. By lime-treatment at the production site one thus avoids the transport of large amounts of water in the form of sludge having a low dry matter contents. Irrespective of the site of mixing it is expedient according to the invention to use a mixture of fatty acid-containing and calcium hydroxide-containing sludge as energy supplement in the production of biogas. In the saponification of fatty acids and notably fatty acid glycerides for use in the method according to the invention it has been found expedient to employ equal molar amounts of calcium and fatty acid(s) . 0A- Two advantages are obtained by thus using about^She \ double stoichiometric amount of calcium (magnesium) ikj Firstly the saponification reaction proceeds ^ and goes to completion to a higher degree than when " using a smaller amount of Ca (Mg). This is probably due to the fact that the base effect of CafOH^ is much higher than the base effect of Ca(OH,fatty acid residue). The pH value of the latter product is 8-9 in aqueous suspension whereas the pH of CafOH^ is 11-12. Moreover, Ca(OH,fatty acid residue) is not soluble in water and this is perhaps the main reason why this substance apparently cannot participate in the further saponification of fatty acid glycerides in an aqueous medium. Secondly, Ca(OH,fatty acid residue) is suspended as very fine particles in biogas reactor sludge, perhaps because of reaction with bicarbonate or carbonic acid, possibly because of a certain polar nature of the substance . Examples of sources of residual grease that may be saponified for use in biogas reactors may be fat scraped off from sewage treatment works, fats from fat traps in the food industry and sludge from clearing tanks as well as many pre-purification plants. Fat-containing sludge from the clearing of tanks in plants which manufacture or work up animal, vegetable and marine oils frequently contains a considerable excess of lecithins. By treatment with lime or slaked lime the lecithins are cleaved whereby 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 in which it may be utilized by the bacteria. Consequently, according to the invention one may expediently use calcium salts of residual grease as a part of the fermenting material in reactors for the production of biogas from organic waste materials. Magnesium salts of fatty acids are just as usable as calcium salts and other sparingly soluble salts with fatty acids for being fermented in rotting tanks includ-ing biogas reactors. Basic magnesium compounds are not ^ as easily accessible in the majority of countries as af'fe I'd basic calcium salts. But in some countries burnt dolo+r . - - Wt- mite (dolomite is a magnesium-calcium carbonate) is usM1 -M W' '-v.'. *&< f: •It'': % I O I .******>. I CJ s 22541 instead of burnt lime and in that case it may be a convenient source for preparing calcium-magnesium soap. The Industrial Utilization of the Invention v.j.^y - 1 '■ ■■■*■■ ■!'— -..I-1 . 5 It is expected that the invention will have particular importance in the economically advantageous disposing of fat-containing wast materials. In the following the invention will be illustrated 10 by some Examples. Example 1 In a biogas reactor having a capacity of 4 50 m , being in stable operation with liquid manure as the sub-15 strate for the fermentation, 250 kg of calcium soap having a fatty acid content of 85%w were introduced. 3 In the reactor 4 00 m of biogas was generated in 4 days beyond the normal production for this reactor of 3 200 m biogas a day. 20 There was no trace of increased foaming, alteration of the pH value or other kinds of disturbance of the operation of the reactor. ( Example 2 j 25 In a biogas reactor having a capacity of 180 m and i being in stable operation with liquid manure as substrate | for the fermentation, 2500 kg of sludge from a fat trap in the drain system from a plant for the deep-frying of onions were introduced. The sludge contained 5% of soya 30 fat having a FFA number (i.e. content of free fatty acids expressed in percent of the fat content) of 50%, ■ the remainder mainly being water. Three hours after the addition there was observed a vigorous foam generation which made it impossible to use the normal system for 35 gas discharge from the biogas reactor. Continuous introduction into the reactor of 25 kg Ca(OH)., stirred into 2500 kg of the same kind of sludge contrarywisc did not cause any formation of foam in the </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 8 reactor and the gas generation proceeded normally with out any inconveniences from foaming and without any vigorous fermentation. ilrj 225414 - 9 - WHAT WE CLAIM IS:

1. A process for the production of a biogas by fermenting organic waste materials in a reactor while adding compounds of at least one alkaline-earth metal, characterized in using calcium soaps and/or magnesium soaps as part of the energy-containing fermenting material fed to the reactor.

2. A process as claimed in claim 1, characterized in feeding calcium salts and/or magnesium salts as a part of the fermenting material fed to the reactor for the production of biogas from organic waste products.

3. A process as claimed in claim 1 or claim 2 , characterized in feeding a mixture of sludge containing fatty acids and calcium hydroxide as part of the feed to a reactor for generating biogas from organic waste materials.

4. A process as claimed in any one of claims 1 to. 3, characterized in feeding a glycerol-containing mixture formed by Ca- and/or Mg-saponification of residual grease or waste products containing oils and fats as part of the feed material to a reactor for generating biogas from organic waste materials.

5. A process as claimed in any one of claims 1 to 4 substantially as herein described with reference to any example thereof.

6. Biogas when produced in accordance with the process of any one of claims 1 to 5. By His/Tkierr aiSffl5Hse3T*gent-—, A.J. PARK & SON Per: < </div>