Investigations of Biomass-based Adsorbents for Carbon Capture in Compression Ignition Engines

Abstract

In this research work, the possibility of using a biomass-based adsorbent for capturing carbon dioxide (CO2) in a compression ignition (CI) engine is explored. For this purpose, coconut shell, rice husk, and eucalyptus wood are selected as feedstocks to prepare activated carbon using carbonization and activation. Coconut shell, rice husk, and eucalyptus wood-activated carbons are termed coconut shell, rice husk, and eucalyptus wood-adsorbents, respectively. As a first step, activated carbon samples are characterized using different sophisticated instruments. Then, a simulation study is performed using three biomass-based adsorbents to examine CO2 adsorption performance. Aspen Adsorption is used to carry out the adsorption and desorption of CO2 in a fixed bed adsorption chamber. The recovery rate, product purity, adsorption duration, breakthrough curve, isosteric heat of adsorption, and energy consumption for regeneration are determined. As investigation on the use of biomass-based adsorbent for CO2 capture by post-combustion method in CI engines is in early stage, few experimentations are performed in a single-cylinder diesel engine which is available in the heat and power laboratory at NIT Rourkela. Therefore, the characterized adsorbent is loaded in an in-house fabricated adsorption chamber and attached to the exhaust of a test engine. A stationary single-cylinder, four-stroke, air-cooled, naturally-aspirated, direct-injection (DI) CI engine developing 4.4 kW at 1500 rpm is used for experimental investigation. The test engine runs on petro-diesel (D100). The maximum adsorption capacity of the adsorbent samples is assessed by adjusting the adsorption gas pressure from 0.5 bar to 2.5 bar at a regular interval of 0.5 bar pressure, and the adsorption temperature is maintained from 25 °C to 75 °C at a regular interval of 25 °C temperature. Experimental investigations are further conducted by varying the adsorbent quantities, viz., 1.25 kg, 2.50 kg, 3.75 kg, 5.00 kg, and 6.25 kg. Hydrocarbon (HC), carbon monoxide (CO), nitric oxide (NO), and CO2 are measured at every load during diesel fuel operation. Then, the parameters related to CO2 capture in the exhaust are evaluated. Nowadays, diesel generators are used in many applications. Therefore, investigations are carried out on CO2 capture using biomass adsorbents in a turbocharged, in-line multi-cylinder, four-stroke, direct-injection (DI) diesel engine generator which is used as a standby power unit to supply electricity to a guest house of an educational institution. The engine develops 62.5 kW and runs at 1500 rpm. Initially, this investigation is carried out on the generator to study emissions and CO2 capture using an adsorbent-filled single adsorption chamber attached to the exhaust of the generator set. Experiments are conducted at different loads using 8 kg, 16 kg, 24 kg, 32 kg, and 40 kg of adsorbents in the adsorption chamber. Exhaust gas temperature and pressure are maintained at 25 oC and 2.5 bar. The adsorption efficiency of adsorbent samples is studied for different adsorption parameters. Adsorbed gas emissions are further captured and stored in a gas bag during regeneration. The captured gas emissions are subjected to Gas Chromatography-Mass Spectroscopy (GS-MC) characterization to evaluate their peak spectra of gas adsorption for adsorbent samples. The adsorption isotherm of adsorbent samples is examined with standard adsorption isotherm models. The kinetics data of the adsorption mechanism is evaluated with adsorption kinetic models. Results reveal that CO2 is reduced by 48% when an adsorption chamber captures CO2 in the exhaust gas than in conventional diesel operation. Further, an attempt is made to reduce CO2 by attaching another adsorption chamber filled with the same adsorbents. Similar experiments are performed on the generator connected to two adsorption chambers. It is observed that CO2 is further reduced by 16%. Complete results are presented in the thesis.