Abstract
Emission of solvent and its degradation products from a typical absorption–desorption based Post Combustion CO2 Capture (PCCC) process is inevitable and thus, an area of growing concern. Recently, it has been pointed out that emissions can also occur by means of aerosol droplets. Conventional counter-measures such as a water wash and a demister are highly effective in reducing vapour based solvent emissions (<5 ppmv), but are ineffective against aerosol based emissions. This manuscript presents the results from the testing of a special demister, Brownian Demister Unit (BDU), as a counter-measure against aerosol based emissions. The BDU consists of a filter element in an isothermal housing and is able to remove very fine droplets (<2 μm) by means of impingement and diffusion. Experiments were carried out at TNO's (Netherlands Organisation for Applied Scientific Research) CO2 capture pilot plant, which has a capacity of capturing 6 tonnes of CO2 per day by means of conventional absorption–desorption. 30 wt.% MEA was used as the solvent for CO2 capture. Emission measurements were mainly performed using an impinger sampling technique across a water wash as well as the BDU. The water wash reduced the MEA emission from about 460 to 250 mg/Nm3 (∼46%) and the BDU reduces the emission levels from about 85–180 mg/Nm3 to 1–4 mg/Nm3 (>97%). The MEA emission levels consisted of both vapour and aerosol droplets. Thus, the water wash is capable of lowering vapour based emissions while, the BDU removes only aerosol based emissions. The measured concentrations of nitrosamines (N-nitrosodimethylamine, NDMA; N-morpholine, NMOR; N-nitrosodiethanolamine, NDELA) in the treated flue gas stream from the absorber are very low and in the order of 10 ng/Nm3. Ammonia emission levels were in the range of 10–70 mg/Nm3. A major disadvantage of the BDU is its high pressure drop. The BDU led to a pressure drop increase of about 50 mbar which is considered to be quite significant considering the total volume of gas to be processed. Based on a rough estimate, the BDU would lead to an increase of 26–52% in the electricity consumption and 1 €/tonne of CO2 in operating cost, for a full scale CO2 capture plant.
