Carbon Dioxide Scrubber 1o5u6u

The biogas scrubbing system The biogas scrubbing system consists of three units, the hydrogen sulfide (H 2S) removing unit, Carbon dioxide (CO2) removing unit, and moisture trapping unit. The three units are interconnected with plastic hoses.

Figure: Biogas Purification, Compression and Bottling Unit Layout Diagram

CO2 scrubbing unit Biogas consists of different gases like Methane, carbon dioxide, and some other trace gases like hydrogen sulfide, hydrogen, nitrogen, water vapor and others. From those gases, only methane is required for cooking and lighting purposes but the others are harmful for the equipments which the biogas burnt in, transported through and decrease the calorific value of the biogas. So that, unwanted gases should be removed using different methods to increase its calorific value of the gas, to safeguard the equipments and to make it easily transportable from production site by compressing into cylinder to usable areas. My interest is not to describe different purification processes and equipments used in this area but to explain about CO 2 scrubbing unit developed by me. The purpose of CO2 scrubbing unit is to remove the unwanted CO 2 from raw biogas dissolving with water. The carbon dioxide scrubbing unit is constructed from reused edible oil plastic drum of volume 25 liters and different out of use plastic bath room materials and a piece of galvanized

pipe. The unit has water inlet, water outlet, raw biogas inlet and purified biogas outlet. The water inlet, gas inlet and gas outlet are positioned at the top whereas water outlet is at the bottom part of the scrubber unit. The gas inlet is connected to the line which is coming from the biogas digester and the gas outlet is to water absorber unit of the system. The water inlet of the scrubbing unit is connected to tap water and the outlet is to discharging port. Even if the water and raw biogas inlets are positioned at the top, there is a 4 cm height difference between them. Inlet of the water is located at the most top place of the scrubber unit but gas inlet is placed below by 4 cm far. So that, both water and raw biogas are forced to enter into scrubber on the top in different ports. The direction in which the raw biogas introduced to the scrubber makes the unit is unique from already known and used in this area. The widely known design is different from this by the direction how the raw biogas enters into the unit. In the known design, the raw biogas is entering into a scrubber from bottom and the water is from top in counter flow direction to the raw biogas. The time of water and biogas in known and used design is smaller than the design which I am developed from local materials. The amount of CO 2 being dissolved in water is determined by the time in which the biogas makes with water and the pressure of the water too. It is possible to increase the time of the gas with water by making them to flow in the same direction from the top to bottom. In my design, both the water and the raw biogas enter into the scrubber unit from the top, and the gas flows along with water down to the scrubber through common line. This is in order to increase the between the gas and the liquid phase mean to give enough time to CO2 being dissolved in the water and forming carbonic acid. Before the purification process starting, the drum should be filled with water up to half level to control escaping of raw biogas through openings. As the raw biogas reaches the bottom of the scrubber, the carbon dioxide (CO2) and Hydrogen sulfide (H2S) gets dissolved in water. So that the gas again bubbled out through water to the top part of the container and this step additionally dissolve the rest CO2 from the raw biogas. Consequently the dissolved CO 2 and H2S are removed from the scrubber through the water outlet. Due to its low density, the purified biogas, methane (CH4) is collected at the top of the water level and es on to the moisture trapping unit for further purification

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CO2 Scrubbing unit

2.1 cm

Water Inlet

Biogas inlet Biogas Inlet

Water outlet

36.2 cm

4.0 cm Biogas Outlet

4.9 cm 2.1 cm 7.6 cm

1.4 cm

45.0cm Water Outlet

Water inlet

4.1 cm 6.0 cm 24.0 cm Biogas Scrubber

Biogas outlet

Figure: CO2 scrubber unit