Parameters and Process Optimisation for Biogas - Revision history

Ranisha at 09:56, 8 April 2015

2015-04-08T09:56:15Z

Ranisha: /* H2S Concentration */

2014-07-07T10:12:23Z

H2S Concentration

Wiki Gardener at 09:08, 18 June 2014

2014-06-18T09:08:35Z

Ranisha: /* Overview */

2014-03-18T11:18:09Z

Overview

Ranisha: /* Overview */

2014-03-18T11:17:01Z

Overview

Frank Helbig: /* Further Information */

2014-01-20T22:26:42Z

Further Information

Frank Helbig: /* Conditioning of Biogas */

2014-01-20T22:26:03Z

Conditioning of Biogas

Frank Helbig: /* Further Information */

2014-01-20T22:25:14Z

Further Information

Wiki Gardener at 18:06, 21 November 2013

2013-11-21T18:06:06Z

Show changes

Wiki Gardener at 13:21, 30 July 2012

2012-07-30T13:21:58Z

@@ Line 1: / Line 1: @@
 = Overview<br/> =
 <u>The metabolic activity involved in microbiological methanation is dependent on the following factors:</u>
 *Substrate temperature
 *Available nutrients
@@ Line 23: / Line 26: @@
 <u>Anaerobic fermentation is in principle possible between 3°C and approximately 70°C. Differentiation is generally made between three temperature ranges:</u>
 *The psychrophilic temperature range lies below 20°C,
 *the mesophilic temperature range between 20°C and 40°C and
@@ Line 38: / Line 42: @@
 The process of bio-methanation is very sensitive to ''changes'' in temperature. The degree of sensitivity, in turn, is dependent on the temperature range. <u>Brief fluctuations not exceeding the following limits may be regarded as still un-inhibitory with respect to the process of fermentation:</u>
 *psychrophilic range: ± 2°C/h
 *mesophilic range: ± 1°C/h
@@ Line 58: / Line 63: @@
 == Batch-type and Continuous Plants<br/> ==
-The retention time can only be accurately defined in [[Types of Biogas Digesters and Plants#Biogas - Digester types|batch-type facilities]]. For [[Types of Biogas Digesters and Plants#Biogas - Digester types|continuous systems]], the mean retention time is approximated by dividing the digester volume by the daily influent rate. Depending on the vessel geometry, the means of mixing, etc., the effective retention time may vary widely for the individual substrate constituents. Selection of a suitable retention time thus depends not only on the process temperature, but also on the type of substrate used.
+The retention time can only be accurately defined in [[Types_of_Biogas_Digesters_and_Plants#Batch_plants|batch-type facilities]]. For [[Types_of_Biogas_Digesters_and_Plants#Continuous_plants|continuous systems]], the mean retention time is approximated by dividing the digester volume by the daily influent rate. Depending on the vessel geometry, the means of mixing, etc., the effective retention time may vary widely for the individual substrate constituents. Selection of a suitable retention time thus depends not only on the process temperature, but also on the type of substrate used.
 <br/>
@@ Line 64: / Line 69: @@
 == Cost Efficiency<br/> ==
-Optimizing the process parameters ''retention time - process temperature - substrate quality - volumetric load'' determine, among others, the [[Economic Viability of a Biogas Plant|cost efficiency]] of the biological processes. But as each m<sup>3</sup> digester volume has its price, heating equipment can be costly and high quality substrates may have alternative uses, the cost-benefit optimum in biogas production is almost always below the biological optimum.
+Optimizing the process parameters ''retention time - process temperature - substrate quality - volumetric load'' determine, among others, the [[Economic_Viability_of_a_Biogas_Plant|cost efficiency]] of the biological processes. But as each m<sup>3</sup> digester volume has its price, heating equipment can be costly and high quality substrates may have alternative uses, the cost-benefit optimum in biogas production is almost always below the biological optimum.
 <br/>
@@ Line 71: / Line 76: @@
 <u>For liquid manure undergoing fermentation in the mesophilic temperature range, the following approximate values apply:</u>
 *liquid cow manure: 20-30 days
 *liquid pig manure: 15-25 days
@@ Line 112: / Line 118: @@
 == Agitation ==
-Many substrates and various modes of fermentation require some sort of [[Agitation of Digesters|substrate agitation or mixing]] in order to maintain process stability within the digester. <u>The most important objectives of agitation are:</u>
+Many substrates and various modes of fermentation require some sort of [[Agitation_of_Digesters|substrate agitation or mixing]] in order to maintain process stability within the digester. <u>The most important objectives of agitation are:</u>
 *removal of the metabolites produced by the methanogens (gas)
 *mixing of fresh substrate and bacterial population (inoculation)
@@ Line 123: / Line 130: @@
 <u>In selecting or designing a suitable means of agitation, the following points should be considered:</u>
 #The process involves a symbiotic relationship between various strains of bacteria, i.e. the metabolite from one species can serve as nutrient for the next species, etc. Whenever the bacterial community is disrupted, the process of fermentation will remain more or less unproductive until an equivalent new community is formed. Consequently, excessive or too frequent mixing is usually detrimental to the process. Slow stirring is better than rapid agitation.
 #A thin layer of scum must not necessarily have an adverse effect on the process. For systems in which the digester is completely filled with substrate, so that any scum always remains sufficiently wet, there is little or no danger that the extraction of gas could be impeded by the scum.
@@ Line 172: / Line 180: @@
 <br/>
 = H<sub>2</sub>S Concentration =
@@ Line 180: / Line 189: @@
 <br/>
 #Adding little O2 to facilitate breaking down of H2S by the small amount of aerobic bacteria residing in the upper crust of digestate mixture.
 #Adding Iron salts (hydroxides and chlorides) to the silage. The iron salt-rich silage needs to be fed in the fermenter on a daily basis so as to enhance the H2S minimizing effect. Chlorides are corrosive and cause problems in the mixing tank. Therefore their use should be limited.
@@ Line 185: / Line 195: @@
 <br/>
 = Conditioning of Biogas<br/> =
@@ Line 215: / Line 218: @@
 The absorptive capacity of the purifying mass depends on its iron-hydrate content: bog iron, containing 5-10% Fe(OH)<sub>3,</sub> can absorb about 15 g sulfur per kg without being regenerated and approximately 150 g/kg through repetitive regeneration. It is noteworthy that many types of tropical soils (laterite) are naturally ferriferous and suitable for use as purifying mass.
-Another de-sulfurization process showing good results has been developed in Ivory Coast and is applied successfully since 1987. Air is pumped into the gas store at a ratio of 2% to 5 % of the biogas production. The minimum air intake for complete de-sulfurization has to be established by trials. Aquarium pumps are cheap and reliable implements for pumping air against the gas pressure into the gas holder. The oxygen of the air leads to a bio-catalytic, stabilized separation of the sulfur on the surface of the sludge. This simple method works best, where the gas holder is above the slurry, as the necessary bacteria require moisture, warmth (opt. 37 C) and nutrients.
+Another de-sulfurization process showing good results has been developed in Ivory Coast and is applied successfully since 1987. Air is pumped into the gas store at a ratio of 2% to 5&nbsp;% of the biogas production. The minimum air intake for complete de-sulfurization has to be established by trials. Aquarium pumps are cheap and reliable implements for pumping air against the gas pressure into the gas holder. The oxygen of the air leads to a bio-catalytic, stabilized separation of the sulfur on the surface of the sludge. This simple method works best, where the gas holder is above the slurry, as the necessary bacteria require moisture, warmth (opt. 37 C) and nutrients.
 In industrialized countries and for large plants, this process has meanwhile reached satisfactory standard. For small scale plants in developing countries, however, using an electric pump becomes problematic due to missing or unreliable electricity supply. Pumping in air with a bicycle pump works in principle, but is a cumbersome method that will be abandoned sooner or later.
 Avoiding de-sulfurization altogether is possible, if only stainless steel appliances are used. But even if they are available, their costs are prohibitive for small scale users.
 == Reduction of the Carbon-dioxide Content<br/> ==
 The reduction of the carbon-dioxide content is complicated and expensive. In principle, carbon-dioxide can be removed by absorption onto lime milk, but that practice produces "seas" of lime paste and must therefore be ruled out, particularly in connection with large-scale plants, for which only high-tech processes like micro-screening are worthy of consideration. CO<sub>2</sub> "scrubbing" is rarely advisable, except in order to increase the individual bottling capacity for high-pressure storage.
 = Further Information =
 *[[Portal:Biogas|Biogas Portal on energypedia]]
 = References<br/> =

@@ Line 171: / Line 171: @@
 <br/>
 = H<sub>2</sub>S Concentration =
-Hydrogen Sulphide results from the transformation of sulphur containing proteins in the plant or animal residues. For the cases where the biogas plants use a <span class="Apple-style-span" style="line-height: normal">[[Combined Heat and Power (CHP)|Combined Heat and Power Engine (CHP)]] for producing heat and electricity, H<sub>2</sub>S can combine with water to form Sulphuric Acid and can hence damage the engine. Further, high concentrations of H<sub>2</sub>S can poison the cell activity thereby reducing the methanation process. Therefore a low concentration (<500 ppm) of the gas is desirable.</span>
+Hydrogen Sulphide results from the transformation of sulphur containing proteins in the plant or animal residues. For the cases where the biogas plants use a <span class="Apple-style-span" style="line-height: normal">[[Cogeneration|Combined Heat and Power Engine (CHP)]] for producing heat and electricity, H<sub>2</sub>S can combine with water to form Sulphuric Acid and can hence damage the engine. Further, high concentrations of H<sub>2</sub>S can poison the cell activity thereby reducing the methanation process. Therefore a low concentration (<500 ppm) of the gas is desirable.</span>
 <span class="Apple-style-span" style="line-height: normal"><u>Following are the measures that can be taken to reduce the concentration of H<sub>2</sub>S in the biogas being sent to the CHP Engine:</u></span>
@@ Line 190: / Line 191: @@
 <br/>
 = Conditioning of Biogas<br/> =

@@ Line 1: / Line 1: @@
 = Overview<br/> =
@@ Line 19: / Line 17: @@
 <br/>
 = Substrate Temperature<br/> =
@@ Line 55: / Line 52: @@
 In order to grow, bacteria need more than just a supply of organic substances as a source of carbon and energy. They also require certain mineral nutrients. In addition to ''carbon, oxygen'' and ''hydrogen'', the generation of bio-mass requires an adequate supply of ''nitrogen, sulfur, phosphorous, potassium, calcium, magnesium'' and a number of trace elements such as ''iron, manganese, molybdenum, zinc, cobalt, selenium, tungsten, nickel'' etc. "Normal" substrates such as agricultural residues or municipal sewage usually contain adequate amounts of the mentioned elements. Higher concentration of any individual substance usually has an inhibitory effect, so that analyses are recommended on a case-to-case basis to determine which amount of which nutrients, if any, still needs to be added.
+<br/>
 = Retention Time<br/> =
@@ Line 95: / Line 92: @@
 == Nitrogen Inhibition<br/> ==
-All substrates contain nitrogen. [[Nitrogen-content and C/N-ratio of organic substrates|Table B2]] lists the nitrogen content of various organic substances and the C/N ratio. For higher pH values, even a relatively low nitrogen concentration may inhibit the process of fermentation. Noticeable inhibition occurs at a nitrogen concentration of roughly 1700 mg ammonium-nitrogen (NH<sub>4</sub>-N) per liter substrate. Nonetheless, given enough time, the methanogens are capable of adapting to NH<sub>4</sub>-N concentrations in the range of 5000-7000 mg/l substrate, the main prerequisite being that the ammonia level (NH<sub>3</sub>) does not exceed 200-300 mg NH<sub>3</sub>-N per liter substrate. The rate of ammonia dissociation in water depends on the process '''temperature and ph value''' of the substrate slurry.
+All substrates contain nitrogen. [[Nitrogen-content_and_C/N-ratio_of_Organic_Substrates|Table B2]] lists the nitrogen content of various organic substances and the C/N ratio. For higher pH values, even a relatively low nitrogen concentration may inhibit the process of fermentation. Noticeable inhibition occurs at a nitrogen concentration of roughly 1700 mg ammonium-nitrogen (NH<sub>4</sub>-N) per liter substrate. Nonetheless, given enough time, the methanogens are capable of adapting to NH<sub>4</sub>-N concentrations in the range of 5000-7000 mg/l substrate, the main prerequisite being that the ammonia level (NH<sub>3</sub>) does not exceed 200-300 mg NH<sub>3</sub>-N per liter substrate. The rate of ammonia dissociation in water depends on the process '''temperature and ph value''' of the substrate slurry.
 <br/>
@@ Line 177: / Line 174: @@
 = H<sub>2</sub>S Concentration =
-Hydrogen Sulphide results from the transformation of sulphur containing proteins in the plant or animal residues. For the cases where the biogas plants use a <span style="line-height: normal" class="Apple-style-span">[[Combined Heat and Power (CHP)|Combined Heat and Power Engine (CHP)]] for producing heat and electricity, H<sub>2</sub>S can combine with water to form Sulphuric Acid and can hence damage the engine. Further, high concentrations of H<sub>2</sub>S can poison the cell activity thereby reducing the methanation process. Therefore a low concentration (<500 ppm) of the gas is desirable.</span>
+Hydrogen Sulphide results from the transformation of sulphur containing proteins in the plant or animal residues. For the cases where the biogas plants use a <span class="Apple-style-span" style="line-height: normal">[[Combined Heat and Power (CHP)|Combined Heat and Power Engine (CHP)]] for producing heat and electricity, H<sub>2</sub>S can combine with water to form Sulphuric Acid and can hence damage the engine. Further, high concentrations of H<sub>2</sub>S can poison the cell activity thereby reducing the methanation process. Therefore a low concentration (<500 ppm) of the gas is desirable.</span>
-<span style="line-height: normal" class="Apple-style-span"><u>Following are the measures that can be taken to reduce the concentration of H<sub>2</sub>S in the biogas being sent to the CHP Engine:</u></span>
+<span class="Apple-style-span" style="line-height: normal"><u>Following are the measures that can be taken to reduce the concentration of H<sub>2</sub>S in the biogas being sent to the CHP Engine:</u></span>
 <br/>
 #Adding little O2 to facilitate breaking down of H2S by the small amount of aerobic bacteria residing in the upper crust of digestate mixture.
 #Adding Iron salts (hydroxides and chlorides) to the silage. The iron salt-rich silage needs to be fed in the fermenter on a daily basis so as to enhance the H2S minimizing effect. Chlorides are corrosive and cause problems in the mixing tank. Therefore their use should be limited.
 #Passing the gas through a scrubber that strips the gas of H2S and brings down the H<sub>2</sub>S level to almost zero ppm. However, this method may involve high initial investment cost for buying scrubber.
 <br/>
 <br/>
 = Conditioning of Biogas<br/> =
@@ Line 228: / Line 226: @@
 <br/>
 = References<br/> =
-<div><references /><br/></div><div><br/></div><div><br/></div>
+<div><references /><br/></div><div><br/></div>
 [[Category:Biogas]]

@@ Line 1: / Line 1: @@
 = Overview<br/> =
-<u>The metabolic activity involved in [[Microbiological Methanation|microbiological methanation]] is dependent on the following factors:</u>
+<u>The metabolic activity involved in microbiological methanation is dependent on the following factors:</u>
 *Substrate temperature
 *Available nutrients

@@ Line 1: / Line 1: @@
 = Overview<br/> =
 <u>The metabolic activity involved in [[Microbiological Methanation|microbiological methanation]] is dependent on the following factors:</u>
-*[[Parameters and Process Optimisation for Biogas#Substrate temperature|Substrate temperature]]
+*Substrate temperature
-*[[Parameters and Process Optimisation for Biogas#Available nutrient|Available nutrients]]
+*Available nutrients
-*[[Parameters and Process Optimisation for Biogas#Retention time|Retention time (flow-through time)]]
+*Retention time (flow-through time)
-*[[Parameters and Process Optimisation for Biogas#PH value|pH level]]
+*pH level
-*[[Parameters and Process Optimisation for Biogas#Nitrogen inhibition and C.2FN ratio|Nitrogen inhibition and C/N ratio]]
+*Nitrogen inhibition and C/N ratio
-*[[Parameters and Process Optimisation for Biogas#Substrate solids content and agitation|Substrat solid content and agitation]]
+*Substrat solid content and agitation
-*[[Parameters and Process Optimisation for Biogas#Inhibitory factors|Inhibitory factors]]
+*Inhibitory factors
-*[[Parameters and Process Optimisation for Biogas#H2S Concentration|H2S Concentration]]
+*H2S Concentration
 <br/>
@@ Line 17: / Line 18: @@
 <br/>
 = Substrate Temperature<br/> =

← Older revision		Revision as of 22:26, 20 January 2014
Line 186:		Line 186:


−	~~= Further Information =~~

		+	<br/>

@@ Line 189: / Line 189: @@
-== Conditioning of Biogas<br/> ==
 Sometimes the biogas must be treated/conditioned before utilization.
@@ Line 197: / Line 198: @@
 <br/>
-=== Reduction of the Moisture Content<br/> ===
+== Reduction of the Moisture Content<br/> ==
 The biogas is usually fully saturated with water vapor. This involves cooling the gas, e.g. by routing it through an underground pipe, so that the excess water vapor condenses at the lower temperature. When the gas warms up again, its relative vapor content decreases. The "drying" of biogas is especially useful in connection with the use of dry gas meters, which otherwise would eventually fill up with condensed water.
@@ Line 203: / Line 204: @@
 <br/>
-=== Reduction of the Hydrogen-sulfide Content<br/> ===
+== Reduction of the Hydrogen-sulfide Content<br/> ==
 The hydrogen sulfide in the biogas combines with condensing water and forms corrosive acids. Water-heating appliances, engines and refrigerators are particularly at risk. The reduction of the hydrogen sulfide content may be necessary if the biogas contains an excessive amount, i.e. more than 2% H<sub>2</sub>S. Since most biogas contains less than 1% H<sub>2</sub>S, de-sulfurization is normally not necessary.
@@ Line 219: / Line 220: @@
 <br/>
-=== Reduction of the Carbon-dioxide Content<br/> ===
+== Reduction of the Carbon-dioxide Content<br/> ==
 The reduction of the carbon-dioxide content is complicated and expensive. In principle, carbon-dioxide can be removed by absorption onto lime milk, but that practice produces "seas" of lime paste and must therefore be ruled out, particularly in connection with large-scale plants, for which only high-tech processes like micro-screening are worthy of consideration. CO<sub>2</sub> "scrubbing" is rarely advisable, except in order to increase the individual bottling capacity for high-pressure storage.

← Older revision		Revision as of 22:25, 20 January 2014
Line 184:		Line 184:

	<br/>		<br/>
		+

	= Further Information =		= Further Information =

−	*

		+	== Conditioning of Biogas<br/> ==
		+
		+	Sometimes the biogas must be treated/conditioned before utilization.
		+
		+	<u>The predominant forms of treatment aim at removing either '''water''', '''hydrogen sulfide''' or '''carbon dioxide''' from the raw gas:</u>
		+
		+	<br/>
		+
		+	=== Reduction of the Moisture Content<br/> ===
		+
		+	The biogas is usually fully saturated with water vapor. This involves cooling the gas, e.g. by routing it through an underground pipe, so that the excess water vapor condenses at the lower temperature. When the gas warms up again, its relative vapor content decreases. The "drying" of biogas is especially useful in connection with the use of dry gas meters, which otherwise would eventually fill up with condensed water.
		+
		+	<br/>
		+
		+	=== Reduction of the Hydrogen-sulfide Content<br/> ===
		+
		+	The hydrogen sulfide in the biogas combines with condensing water and forms corrosive acids. Water-heating appliances, engines and refrigerators are particularly at risk. The reduction of the hydrogen sulfide content may be necessary if the biogas contains an excessive amount, i.e. more than 2% H<sub>2</sub>S. Since most biogas contains less than 1% H<sub>2</sub>S, de-sulfurization is normally not necessary.
		+
		+	For small- to mid-size systems, de-sulfurization can be effected by absorption onto ferric hydrate (Fe(OH)<sub>3</sub>), also referred to as bog iron, a porous form of limonite. The porous, granular purifying mass can be regenerated by exposure to air.
		+
		+	The absorptive capacity of the purifying mass depends on its iron-hydrate content: bog iron, containing 5-10% Fe(OH)<sub>3,</sub> can absorb about 15 g sulfur per kg without being regenerated and approximately 150 g/kg through repetitive regeneration. It is noteworthy that many types of tropical soils (laterite) are naturally ferriferous and suitable for use as purifying mass.
		+
		+	Another de-sulfurization process showing good results has been developed in Ivory Coast and is applied successfully since 1987. Air is pumped into the gas store at a ratio of 2% to 5 % of the biogas production. The minimum air intake for complete de-sulfurization has to be established by trials. Aquarium pumps are cheap and reliable implements for pumping air against the gas pressure into the gas holder. The oxygen of the air leads to a bio-catalytic, stabilized separation of the sulfur on the surface of the sludge. This simple method works best, where the gas holder is above the slurry, as the necessary bacteria require moisture, warmth (opt. 37 C) and nutrients.
		+
		+	In industrialized countries and for large plants, this process has meanwhile reached satisfactory standard. For small scale plants in developing countries, however, using an electric pump becomes problematic due to missing or unreliable electricity supply. Pumping in air with a bicycle pump works in principle, but is a cumbersome method that will be abandoned sooner or later.
		+
		+	Avoiding de-sulfurization altogether is possible, if only stainless steel appliances are used. But even if they are available, their costs are prohibitive for small scale users.
		+
		+	<br/>
		+
		+	=== Reduction of the Carbon-dioxide Content<br/> ===
		+
		+	The reduction of the carbon-dioxide content is complicated and expensive. In principle, carbon-dioxide can be removed by absorption onto lime milk, but that practice produces "seas" of lime paste and must therefore be ruled out, particularly in connection with large-scale plants, for which only high-tech processes like micro-screening are worthy of consideration. CO<sub>2</sub> "scrubbing" is rarely advisable, except in order to increase the individual bottling capacity for high-pressure storage.
		+
		+	<br/>

@@ Line 177: / Line 177: @@
 = H<sub>2</sub>S&nbsp;Concentration =
-Hydrogen Sulphide results from the transformation of sulphur containing proteins in the plant or animal residues. For the cases where the biogas plants use a <span class="Apple-style-span" style="line-height: normal">'''Combined Heat and Power Engine (CHP)''' for producing heat and electricity, H<sub>2</sub>S can combine with water to form Sulphuric Acid and can hence damage the engine. Further, high concentrations of H<sub>2</sub>S can poison the cell activity thereby reducing the methanation process. Therefore a low concentration (<500 ppm) of the gas is desirable. <u></u></span>
+Hydrogen Sulphide results from the transformation of sulphur containing proteins in the plant or animal residues. For the cases where the biogas plants use a <span class="Apple-style-span" style="line-height: normal">[[Combined_Heat_and_Power_(CHP)|'''Combined Heat and Power Engine (CHP)''']] for producing heat and electricity, H<sub>2</sub>S can combine with water to form Sulphuric Acid and can hence damage the engine. Further, high concentrations of H<sub>2</sub>S can poison the cell activity thereby reducing the methanation process. Therefore a low concentration (<500 ppm) of the gas is desirable.</span>
 <span class="Apple-style-span" style="line-height: normal"><u>Following are the measures that can be taken to reduce the concentration of H<sub>2</sub>S in the biogas being sent to the CHP Engine:</u></span>
@@ Line 186: / Line 186: @@
 #Adding Iron salts (hydroxides and chlorides) to the silage. The iron salt-rich silage needs to be fed in the fermenter on a daily&nbsp;basis &nbsp;so as &nbsp;to enhance &nbsp;the H2S minimizing effect. Chlorides are corrosive &nbsp;and&nbsp;cause problems in the mixing tank. Therefore their use should be limited.&nbsp;
 #Passing &nbsp;the &nbsp;gas &nbsp;through &nbsp;a &nbsp;scrubber &nbsp;that &nbsp;strips &nbsp;the &nbsp;gas &nbsp;of H2S &nbsp;and &nbsp;brings&nbsp;down the H<sub>2</sub>S level to almost zero ppm. However, this method may involve high initial investment cost for buying scrubber.