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Biogas purification at Mapocho WWTP

2021-10-04 11:34:03

Biogas is a mixture of gases, the main components of which are methane and carbon dioxide, produced as a result of the fermentation of organic matter in the absence of air by the action of a microbial consortium (anaerobic digestion).

The composition of the biogas depends entirely on the nature of the waste used and the conditions under which anaerobic digestion is carried out. Generally, the biogas is used for energy recovery, which is determined by the methane concentration. However, a purification of certain contaminants with abrasive and corrosive character, such as siloxanes and H₂S, is necessary to ensure a correct operation of the cogeneration engines.

The Mapocho-Trebal wastewater treatment plant (WWTP), located in Santiago de Chile, treats 30% of the town's water and is a benchmark facility. The facility uses biogas energy by means of three cogeneration engines, each with a power of 1,000 kW. Normally two of these are in operation, while the third is reserved for maintenance stops.

The strict legislation of the trans-Andean country regarding emissions of volatile organic compounds (VOCs) and nitrogen oxides, and the need to obtain an effluent free of mainly siloxanes and H2S for a correct use of the purified biogas, led those responsible for the WWTP to contact BION.

Our technical department studied the case in depth and proposed to implement a competitive alternative both in economic and technical terms.

Plant data

The biogas purification system consists of two parallel analogous lines composed of three filters in series.

Biogas flow rate: 3600 m3/h.
H₂S concentration: H₂S concentrations, due to biogas pre-treatment, range from 40 to 60 ppmv. In specific cases where the pre-treatment does not work properly, peaks of up to 500 ppmv have been measured. The objective is to reduce these values to concentrations below 1 ppmv.
Siloxanes: An exhaustive characterization of the siloxanes present in the biogas stream revealed significant concentrations of cyclic siloxanes type D3, D4 and D5 among others. Values of up to 10 mg/m³ were measured for the D5 type.
Others: in addition to the compounds, significant concentrations of mercaptans, cycloalkanes, chlorinated compounds and aromatic hydrocarbons were measured.

Solution

After a thorough characterization of the biogas to be treated and an assessment of the working conditions, the solution proposed by BION was as follows:

High quality Active Carbon for the removal of high molecular weight VOCs and siloxanes.

High quality Bion KOH to improve the removal of H₂S, certain VOCs and mercaptans.

The solution proposed by BIOCONSERVACION was successful, generating biogas with H₂S levels below 1 ppm.

BION's collaboration continues once the solution has been implemented and the results have been verified, since it has the possibility of carrying out an analysis of the condition of the socks prior to their replacement. By evaluating the remaining capacity of the media, it is able to optimize the process to achieve maximum utilization of the potential of each installation.

In our blog...

Efficient H2S Removal in Biogas

The cost of removing H2S from biogas involves much more than just the cost of the media itself.Using a media with a higher absorption capacity result in fewer media replacements, which means savings in the total quantity of media consumed, fewer media replacements, and lower yearly disposal costs. With BION CARB BG, Relative Humidity Will no Longer be a Problem. Relative humidity in biogas installations can vary substantially depending on plant conditions. BION CARB BG catalytic carbon is designed to work under optimal conditions with relative humidities between 30% and 95%, making it a very versatile product. Lower Cost per kg of H2S Removed H2S is a corrosive gas that causes major damage to equipment. BION CARB BG has an H2S elimination capacity of up to 50% by weight, which makes it highly cost-effective compared to other alternatives on the market. High Absorption Capacity Working with a product that has up to 50% absorption capacity is synonymous to significant improvements in OPEX since the costs associated with the replacement of the average are lowered, such as: - Operator cost - Replacement cost - Disposal cost - Inert gas consumption - Cost of plant shutdowns in case of a single vessel

Protect your biogas installations and reduce the maintenance costs

The conversion of biogas into green energy is not only environmentally friendly, but also contributes to the optimization of natural resources. More and more industries have biogas stations to take advantage of waste generated in these facilities, contributing to generate a circular economy where all available resources are exploited. Biogas plants need to remove impurities before it is diverted to its final use (upgrading or cogeneration engines). In the case of upgrading, the need for purification is high due to the strict conditions required for methane purity. The BION media ensures an effective removal of impurities at 99.5% efficiency. BION medias: Protect and maintain the compressor by preventing the occurrence of corrosive atmosphere inside the compressor. Protect the membranes against fouling or pore blockage. Have very high adsorption capacity They are specially designed to give high performance in environments with low oxygen levels. Protect and maintain the installations This becomes to reduced operating and maintenance costs and increased sorbent or adsorbent lifetime. BION biogas purification solutions are the best return on investment because they They remove pollutant gases before they cause irreversible damage to membranes, compressors or cogeneration equipment. Enables compliance with biomethane grid injection input requirements Extends the lifetime of the pretreatment stage by reducing operating costs Avoid downtime by preventing costly unexpected repairs Eliminate ALL common contaminants other than H2S.

Biogas Desulfurization at ETAR do Norte (Portugal)

The Wastewater Treatment Plant (ETAR) do Norte is one of the largest in the central region of Portugal, serving several municipalities. The infrastructure is located in the area of Coimbra, Leiria, occupying 6 hectares of land; it receives effluents from about 250,000 inhabitants of several municipalities. It has the capacity to treat some 38,000 m3 of wastewater daily, of which 77% is domestic, 18% from industry and 5% is other effluents. The biogas resulting from treatment is used as fuel for a cogeneration plant, where energy recovery is maximized through combined heat and power production. The thermal energy is used to heat the sludge digesters, the building and the domestic hot water. The electrical energy produced, which can reach an output of 1.2 MW, is sold to the national power grid. Biogas Desulfurization Iron filings, one of the most widely used traditional methods, were used to reuse biogas for energy recovery. However, high construction costs and low efficiency led Simlis to look for other technologies to improve its process. As an alternative, BION together with its distributor in Portugal, Equifluxo, proposed the use of BION Fe, a filter media regenerable with ambient air, capable of reaching a H2S removal capacity of up to 45% w/w. The use of this media would provide the following advantages over iron filings: Save adding an iron chloride solution as a step prior to desulfurization. Reduce the number of media changes due to its high desulfurization capacity (45% w/w of BION Fe versus 12% w/w of iron filings). Achieve higher efficiencies. Reduce energy consumption due to the low pressure drop values generated. Depending on the final composition of the spent product and the regulations of each country, BION Fe could even be recoverable. On the other hand, the removal of water from the biogas, besides serving to promote the optimal operation of BiON Fe, has other advantages. The drying of the gas allows optimizing the combustion process in the cogeneration engine, reaching values between 2 and 5% more energy generation; it increases the efficiency of the engine and reduces the gas/fuel consumption; it allows reducing the contamination of the engine oil with the condensate, extending the life time of the oil from 400-500 hours to 2000-3000 hours. Finally, in the case of treating biogas with siloxanes, this dehumidification stage will help to slightly reduce the concentration of some of these recalcitrant compounds. Bioconservacion Solution BION designed a reactor for biogas treatment with the following characteristics: Flow rate: 25 m3/h Temperature range: 35-40 ºC Relative humidity: 95-99 %. Composition: CH4 66 %, CO2 30 %, H2S 2500 ppm To carry out biogas desulfurization, Bioconservacion/Equifluxo designed a very versatile unit with a double fiberglass wall to reduce the effects of condensation, with a plenum that avoids the generation of preferential paths and therefore the use of the entire medium, as well as the generation of high pressure drop values. Over a period of 12 months, Bioconservacion/Equifluxo carried out exhaustive monitoring of the equipment's results, with technical visits every 45 days for the first 3 months and every 3 months thereafter. The results obtained were very positive, reaching efficiencies of over 99%, allowing full use of the energetic power of biogas (Figure 2). Evolution of H2S concentration at the reactor inlet/outlet over time.

In our blog...

Efficient H2S Removal in Biogas

Protect your biogas installations and reduce the maintenance costs

Biogas Desulfurization at ETAR do Norte (Portugal)

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