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With the increasing need for sustainable energy, biogas has greatly gained interest in the last few years. Originating from the process of anaerobic fermentation, biogas can be used to numerous applications to reduce green house gas emissions and produce clean sustainable energy [1].
Biogas is typically composed of methane (CH4) and carbon dioxide (CO2), but also contains traces of additional gases, such as hydrogen sulphide (H&#;S), ammonia (NH3), hydrogen (H2) and other impurities.
Due to its highly corrosive nature, H&#;S needs to be stripped off with upgrading technologies in order to preserve expensive biogas processing equipment. Even with low H&#;S concentration, metal corrosion will be slower, but will still occur due to the presence of carbon dioxide [2].
Here is an introductory video on gas desulphurization from DMT, featuring their own solution: the Sulfurex®.
Selecting the Best Technology for your System
What are the factors for selecting technologies for H&#;S removal? When it comes to evaluating a potential H&#;S removal technology, you need to consider three important variables: your site&#;s conditions, the product gas requirements and the economics [4].
Sites Conditions
Every installation is different. Whether for inlet gas flow or operating parameters, your biogas facility has its own specific conditions. The amount of H&#;S processed per day, temperature, pressure, oxygen concentration, carbon dioxyde and water content of your system should and will directly influence your decision.
Product Gas Requirements
According to the gas utility you are doing business with, each structure has unique pipeline injection specifications. What are the environmental air permitting regulations? How will SO&#; be released? Make sure to answer these questions before settling in on a solution.
Economical Benefits
Last but not least, economical benefits. How do I get the most of my investment? Ultimately, it comes down to CAPEX against OPEX tradeoff. A more expansive technology may require less operating and maintenance fees, whereas a cheaper solution could lead to bigger ongoing expenses.
Based on your site parameters, here is a table below to help you select an economical H&#;S abatement technology for your application.
SCFM: Standard cubic feet per minute of biogasAs every single biogas upgrading installation requires an H&#;S removal solution, there are a great number of technologies available on the market worldwide. Here you will find the best solutions from various BiogasWorld members.
Biogas Desulphurisation Systems Available on the Market
DMT&#;s Sulfurex® BR, CR & BF
DMT has developed a vast amount of biogas treatment technologies. For the key biogas contaminants, DMT can offer one or a combination of technologies to economically manage them. A technology selection is made by analyzing the mixture of contaminants, the gas flow, the pollution load and the application. By not pushing one technology, DMT can provide the customer with the best solution for that specific project.
The basic principle of the technologies DMT offers to desulfurize gas, is the absorption of H&#;S to a liquid. An oxidation process converts the H&#;S to elemental sulfur or sulfate. DMT offers a pure chemical process Sulfurex®CR (Chemical Reaction), a biological process Sulfurex®BF (Biotrickling Filter), and a biochemical process Sulfurex®BR (Biological Regeneration) with integrates a bioreactor for the biological regeneration of the solvent.
For more information Sulfurex® technologies, click here.
Benefits
Paques THIOPAQ® &#; Biogas desulfurization
Highly Efficient H2S Removal from biogas and landfill gas at high uptime enables industries to consistently meet stringent gas quality requirements.
The THIOPAQ® was developed by Paques, in cooperation with universities, research institutes and customers. It can be applied to a wide range of biogas streams containing H&#;S and can be combined with all biological anaerobic systems. The &#;caustic&#; solution in the THIOPAQ® scrubber is continuously biologically regenerated. In the scrubber, the gas containing
H&#;S is brought into contact with the washing water in counter currently. Absorption of H&#;S under slightly alkaline conditions (pH 8-9) enables a chemical reaction with hydroxide ions.
Through continuous development Paques is able to provide every customer with a tailor-made gas treatment solution that enables the customer to produce biogas with a very low hydrogen sulfide content at a low O&M cost and to fuel local gas-fired microgrids, or upgrade the gas to biomethane. Additionally, the elemental sulfur produced by the THIOPAQ® can be used as a high-quality fertilizer.
For more information on THIOPAQ® , click here.
Benefits
Prodeval&#;s VALOPACK
After a first pretreatment process, the VALOPACK filtration unit is designed to extract pollutants (H&#;S, siloxanes, VOCs) from Biogas before continuing with the upgrading process, using two activated carbon filter tanks.
There is also a 3 µm dust filter located after the activated carbon filters, preventing dust from spreading after load changes.
The type of activated carbon is chosen based on the concentration of each pollutant in the Biogas (dealing specifically with H&#;S or VOCs).
For more information on VALOPACK, click here.
Benefits
Pyro Green-Gas Desulfurization System
Pyro Green-Gas offers two desulfurization processes. The Ferrachel II® Iron chelate process for high gas flows and high inlet hydrogen sulfide concentrations. Dry scrubbing catalyst for low inlet hydrogen sulfide concentrations. In cases where hydrogen sulfide concentrations of less than 100 ppmv are required, a dry scrubbing catalyst stage is required.
Pyro Green-Gas (previously Air Science Technologies) offers many desulfurization processes tailored to balance CAPEX and OPEX for specific gas flows and conditions. Broadly there is dry desulfurization; either via a catalytic redox reaction onto media or adsorption, and there is absorption where the gas contacts a curated absorbing liquor where chelated iron interacts with and removes hydrogen sulfide from the gas. The latter is particularly well suited for large flows and highly sour gas.
For more information Pyro Green-Gas desulfurization systems, click here.
Ferrachel II® Iron Chelate Process
The process operates continuously and only requires a periodical inspection and cleaning of some internal components to ensure optimum efficiency and performance.
For outlet requirements of less than 100 ppmv, the Iron Chelate desulfurization process can be followed by a dry desulfurization step which can bring hydrogen sulfide concentration down to &#; 4 ppmv.
Dry Scrubbing Catalyst (DSC) Process
The process consists in passing the hydrogen sulfide charged gas through a tower filled with the required amount of active media for the required hydrogen sulfide outlet concentration over the design life of the media.
Generally, two towers are installed with inter connecting piping and valves to operate each tower in a lead or lag mode. This feature allows for the optimal use of the desulfurization media and minimizes the operating cost of the desulfurization process.
UGN Gas Desulphurisation Systems &#; BEKOM H
The untreated, warm and humid biogas flows through the filter module that is filled with UgnCleanPellets®. The hydrogen sulphide is targeted and completely removed from the raw gas and transformed to elemental sulphur.
Atmospheric oxygen is fed in to allow the filtering material to self-regenerate, while the desulphurisation process is running at the same time. This ensures that the desulphurising capacity of the material is maintained for a long time. When the pellets reach their maximum take-up capacity, the hydrogen sulphide content in the clean gas increases gradually.
For more information on BEKOM H, click here.
Benefits
Want more information on Desulfurizer? Feel free to contact us.
Veolia&#;s SULFOTHANE&#;
The Sulfothane&#; process consists of two steps. First it resembles a chemical alkaline scrubber for H&#;S . Second the alkaline solution is continuously regenerated in a biological process using aerobic sulphur bacteria.
Sulfothane&#; uses a widely applied and well proven technology to treat gas streams containing up to 50,000 ppm H&#;S . The scrubber column is operated in counter current mode, which results in very high removal efficiency of H&#;S. Even lower than 25 ppm H&#;S is possible, exceeding 99%. The process reduces the odour, toxicity and corrosiveness of the biogas, without dilution with air due to a strict separation of biogas and aeration steps.
For more information on SULFOTHANE&#; , click here.
Benefits
BGasTech&#;s BTS-MPdry
Biogas conditioning/cleaning technology (BTS-MPdry) from Biogas & Gases Technologies (BGasTech) is a range of technologies applied for biogas cleaning. It includes: the BTS-Siloxa technology for the removal of siloxanes and the BTS-Sulfure technology for the removal of H2S in biogas. Both are based on dry removal methods.
As a cleaning technology it is based on a combination of removal techniques and has two basic stages.
Stage 1: Coarse. Cooling-condensation.
Stage 2: Fine. Adsorption on activated carbon.
For this purpose, it has a set of interconnected equipment that allows the elimination of moisture content and siloxanes by physical means (thermal and adsorption), halogenated compounds and H2S, as well as reducing the gas temperature to permissible values for engine intake.
For more information on BTS-MPdry, click here.
Benefits
The BgPur system is a proven solution for biogas treatment from anaerobic digesters and landfill. The system reduces hydrogen sulfide (H&#;S) concentrations and converts it to solid elemental sulfur for resale. The system uses a liquid chemical catalyst, compact gas/liquid contactor, and solids removal system and does not consume the chemical catalyst driving the conversion of H&#;S to sulfur, minimizing chemical make-up requirements. As a result, operating costs are significantly lower than typical solid sorption processes and the system promotes a stable and predictable H&#;S removal process.
For more information BGPUR&#;, click here.
Benefits
Iron Oxides for H&#;S Removal
UgnCleanPellets®
UGN Umwelttechnik Ltd offers a natural desulphurization adsorbent which is engineered and produced in Germany and already utilized in hundreds Biogas sites worldwide (reference in US available). The adsorbent UgnCleanPellets® is applied in external desulphurization processes and has the property making raw and fine purification process in one step. It is possible, reducing H&#;S loads in one purification reactor from ~ ppm below < 5, depending on gas conditions, composition, and flow.
For more information on UgnCleanPellets®, click here.
Benefits
AxTrap&#; Series Sulfur Removal Adsorbents for Biogas
Axens offers the AxTrap&#; Series of dry, granular media scavengers to safely and effectively remove these common sulfur contaminants.
AxTrap&#; Series products are based on patented, proprietary mixtures of iron oxides and/or mixed metal oxides &#; on an inert, inorganic carrier. The result is a particularly robust, granular material in which the metal oxide matrix provides a firmly bound active phase which is non-toxic, non-hazardous, non-pyrophoric and environmentally safe in both fresh and spent condition.
Benefits
For more information on AxTrap&#; Series, click here.
Promindsa&#;s MICRONOX BIOX
MICRONOX ON16 is a mixture of iron oxides-hydroxides and other functional oxides specially developed to be added directly into the fermentation reactor This product has been the object of extensive preliminary studies, with successful application in biogas plants. It reacts with hydrogen sulfide to generate iron sulfide and sulfur. Both elements are common components of fertilizers leading to improved properties.
Benefits
For more information on MICRONOX BIOX, click here.
Notes & Sources
[ ] Cong Xiao et al. (, December). Review of desulfurization process for biogas purification. School of Environmental Science and Engineering, Qilu University of Technology, Jinan, Shandong, China.
https://www.researchgate.net/publication/_Review_of_desulfurization_process_for_biogas_purification
[ ] Ibid.
[ ] Daniel Waineo, DW. (, February). H2S Removal from Biogas for RNG and Electricity Projects [H2S Safety Issues]. American Biogas Council. https://americanbiogascouncil.org/wp-content/uploads//03/H2S-removal.pdf
[ ] Michael Knapke, MK. (, September). Technologies for Hydrogen Sulfide Removal [Selection of a potential H2 S Removal Technologies]. RNG Works , Guild Associates.
[5] Xiao Yuan Chan et al. (, February). Membrane gas separation technologies for biogas upgrading. Laval University and Ho Chi Minh City University of Technology and Education. https://www.researchgate.net/publication/_Membrane_gas_separation_technologies_for_biogas_upgrading
[6] BGasTech (March, ). Desulfuration of Biogas. Biogas & Gases Technologies. https://bgastech.com/en/desulfuration-of-biogas/
[7] Joaquín Reina Hernández. (). Origin, Effect and Treatments. [Biogas cleaning. Hydrogen sulfide removal]. BGasTech.
[8] BioEnergy Consult (May, ). Methods for Hydrogen Sulphide Removal from Biogas. https://www.bioenergyconsult.com/hydrogen-sulphide-removal-from-biogas/
Sulfur as an element is ubiquitous. In the universe, it ranks 10th inprevalence; on the earth, it comes in fifth. It is found in vitamins, amino acids, the earth&#;s crust, and virtually every plant and animal. There are myriad uses of sulfur in industry and agriculture, including herbicides, pesticides and fertilizers. Needless to say, it is a critical element in nature and in the economy. Nevertheless, when present in certain chemical compounds and mixtures, sulfur does not play well with others. These compounds can be hazardous to health; damaging to the ecology; and corrosive to many materials utilized for industrial purposes. The organisms and matter where these dangerous compounds are found must be subject to the desulfurization process.
The desulfurization meaning is actually two-fold: it could refer to removing elemental sulfur at the molecular level or, alternatively, extracting sulfur compounds from chemical mixtures. On its own, sulfur can be extricated from subterranean deposits by melting it through the injection of water heated above the boiling point. Once melted, the sulfur is piped out to the surface. Simple enough. What, though, about those dangerous compounds that find themselves in diverse compositions like natural gas, biomass and petroleum, for instance? What does desulfurization look like when the element is bonded to others?
Natural gas formations exist all over the world. The largest deposits are located in the Middle East, the Russian Federation and Europe. In North America, natural gas is most abundant in Texas, Oklahoma, New Mexico, Wyoming, and Louisiana. In the United States, over 50 percent of homes are heated by natural gas and this fuel accounts for 24 percent of energy use overall. Natural gas is also a constituent ingredient of many paints, plastics and even medicines. Propane gas &#; popular with avid grillers and barbecue enthusiasts &#; is also derived from natural gas.
Natural gas is often retrieved from its earthen deposits in the same manner as petroleum &#; through drilling or hydraulic fracturing. Sometimes a &#;horse head&#; pump is employed to draw both natural gas and oil to the surface. This resource is found in shale formations, coal beds and sandstone. Once the gas is drawn from its source, it is transported via 300,000 miles of pipeline to locations throughout the U.S., eventually available to customers. Before this lengthy trip, however, the gas must be treated to remove the hydrogen sulfide (H2S) and carbon dioxide (CO2).
The desulfurization of natural gas is necessary for two very important reasons. The H2S that is present is not only toxic to workers and consumers but it is also detrimental to the very pipeline networks that deliver the fuel. At its worst, it can induce respiratory failure, coma and even death to those exposed. Meanwhile, it can quickly oxidize the metal interiors of natural gas pipelines, thereby damaging their safety and overall efficiency. Therefore, natural gas needs treatment at a desulfurization plant soon after its retrieval from wherever it is deposited.
If hydrogen sulfide presence surpasses 5.7 milligrams per cubic meter of natural gas, the gas passes a threshold from user-grade to &#;sour&#; gas. Under such a circumstance the gas is ordinarily run through a tower or column that contains amine, i.e. a derivative of ammonia. The amine solution absorbs the H2S compound as the gas stream passes through, leaving a purer effluent natural gas in its wake. The amine solution is available for further use over many cycles of H2S removal. This procedure for H2S removal is performed in the vast majority of occasions when hydrogen sulfide absorbtion is necessary.
Essentially, biogas is the methane (and CO2) that gets released from organic matter under anaerobic &#; or oxygen-deprived &#; conditions. This can take place naturally, as at the core of a compost heap or landfill, or it can be induced by human technology, i.e. engineered anaerobic digesters. Absent oxygen, bacterial micro-organisms operate on the organic material, breaking it down so that biogas is released from the solids that had retained it. The material is as diverse as sewage, food waste, compost, wastewater, rotting vegetation and animal manure. Once captured, the biogas powers combustion engines which, subsequently, charge electrical generators. Biogas can provide energy to vehicles, farms, neighborhoods and even public transit systems.
Still, biogas, too, has an H2S problem, the very same problem evident with natural gas. The public health threat and infrastructure impairment are equally real with biogas production. Fortunately, biogas desulfurization is available by means of two distinct methods.
1. Wet de-sulfurization &#; can be further broken down into three versions:
2. Dry de-sulfurization &#; rather than using a solvent or solution, dry de-sulfurization utilizes powder/particle agents to treat the biogas. Doing so minimizes the possibility of corrosion in the biogas tank. In general, this method works better when sulfur content is on the low side.
Once properly purified, biogas is an unsung hero of renewable fuels. Not only is it environmentally friendly and cost-effective, it answers a large part of the seemingly eternal waste management question.
Hydrogen sulfide is not the only problematic sulfur compound in energy production. Sulfur dioxide (AO2) is emitted from exhaust flues at energy plants that burn fossil fuels and facilities that incinerate solid wastes. In nature, SO2 is released when volcanoes erupt. On a smaller scale, it is emitted whenever a match is lighted. Implicated in acid rain, SO2 is a major air pollutant that affects habitat livability and the survival of various plant and animal species.
How does flue gas desulfurization work? As with the categories noted above, there are multiple ways to do this. One such procedure is wet scrubbing. This involves an alkaline absorbent slurry &#; limestone, lime or even seawater &#; that is sprayed directly on the gas stream or pooled to receive the stream. At other times the slurry is converted to powder by means of hot gas. When the flue gas makes contact with the particles, a similar reaction removes the sulfur molecules. This method is known as spray-dry scrubbing. Other means of flow gas desulfurization are employed depending on sulfur content and related factors. Like atmospheric CO2 scrubbers, these treatments isolate the SO2 from the flue gas stream before it is released into the air.
The atmospheric residue desulfurization process helps to keep toxic particulates from doing damage to ecosystems and the air we breathe. The various methods heretofore mentioned take place in an atmospheric residue desulfurization unit where not only sulfur dioxide, but nitrogen oxides and other particulates are captured and isolated.
Many of the agents responsible for neutralizing H2S can separate the sulfur from its compounds. However, research demonstrates that an iron oxide sold sponge &#; i.e. wood shavings infused with iron, or ferric, oxide &#; is effective in hydrogen desulfurization by first absorbing the H2S, and then converting ferric oxide into ferric sulfide. The ferric sulfide subsequently reverts to ferric oxide after releasing elemental sulfur.
Adsorptive Desulfurization is an innovative technique that has transformed the way we address the presence of sulfur in gas streams. At Gazpack, we pride ourselves on leveraging cutting-edge technology such as Adsorptive Desulfurization to remove sulfur from a variety of gases. This process involves adsorbents like zeolites, activated carbons, or metal-oxides that selectively trap sulfur compounds, resulting in a cleaned gas stream. Importantly, Adsorptive Desulfurization provides a more efficient, economical, and environmentally friendly alternative to conventional desulfurization methods, particularly when dealing with gas streams containing low concentrations of sulfur.
Energy sources with less CO2 emission than traditional fossil fuels promise greater energy independence and a cleaner environment. Yet even these gases have contaminants that require removal before they are burned for electrical generation or combusted for vehicular performance. The good news is that technology (desulfurization plant) provides for the removal of sulfur compounds before the energy is consumed.
For more information, please visit High Purity Silica Sand.