Ammonia a base compound used in chemical process industries to produce the commercial chemical product. Produced in large-scale from synthesis gas that in-turn generated from natural gas, naphtha or fossil sources rich in hydrogen content.
Existing process technologies obtain hydrogen from fossil chemicals and nitrogen from the air. These two compounds are reacted in a reactor to produce ammonia. However, if the source for this process is obtained other than fossil chemicals then ammonia production too, becomes green technology.
Project on this concept helps to develop a system that uses biogas as a raw material and develop a supply chain link to waste treatment problems and fertilizer production. Methane content in biogas is about 60-70 percent approximately depending on the biomatter. Hydrogen can be obtained from methane by partial oxidation or auto-thermal processes to generate synthesis gas containing carbon monoxide and hydrogen. Nitrogen supplied from the air during the above process is sufficient in composition for ammonia reaction on a catalyst. However, carbon dioxide and carbon monoxide should be removed to maintain the feed ratios.
Design engineers, process engineers, chemical engineers and industrial engineers can build up project report regarding this concept. If the design is successful than it could change the production of ammonia from large-scale to small-scale with less energy consumption moreover turning the process into green technology.
A unit operation that may be used in the process sequence of ammonia production from biogas:
- Biogas digester: organic matter cutting, slurry formation ( culture, pH).
- Biogas purification or upgradation: MEA or KOH absorption and even PSA.
- Syngas production: Dry reforming or autothermal reforming.
- Carbon dioxide removal by absorption: K2CO3 absorption and stripping.
- Ammonia reactor: Fixed bed catalytic reactor.
- Ammonia purification and storage: Purging and refrigeration system
The bottleneck of the process can be identified at the syngas production and carbon dioxide recycling steps. These two steps govern the heat requirement and CO2 emission from the process. By process simulation, an optimistic method can be identified. ASPEN plus or CHEMCAD are sophisticated and well equipped with simulation tools and packages.
Selection of catalyst:
For autothermal, reforming of biogas catalyst selection is vital; the cost of ammonia production includes the catalyst life for reaction cycles. A highly durable catalyst is best to choose and of it is Ni-based monolithic substrate. It is strong and does not be affected by the hydrogen sulphide and siloxanes present in the biogas.
Conceptual process flow diagram:
Ammonia production flow diagram description:
Biomass or organic waste is treated and fed to bio-digester. Biogas produced by the microorganism in the digester majorly contains methane and carbon dioxide. A blower pumps the gas from digester collecting hood to carbon dioxide absorption column. K2CO3 absorbs the CO2 and CO and sends out methane-rich gas to a synthesis converter to generate Hydrogen-rich gas. The outlet is passed to the carbon molecules separation membrane to separate unreacted methane and generated carbon dioxide and carbon monoxide from hydrogen and nitrogen. Ammonia converter contains catalyst beds to support the reaction of hydrogen and nitrogen to produce ammonia. Ammonia collected in the storage tanks and used for fertilizer manufacturing. This model diagram is an idea to develop a sustainable process that helps to maintain organic matter conservation and recycle nitrogen to prevent a shortage of nitrogen-based fertilizers.