Save water with CO2Scrub

26 June 2015

In many countries and regions, the focus on reducing the use of water and other utilities is not just driven by individual companies’ wish to have an ever greener profie. There is a growing trend that sees new political initiatives and restrictions being launched, and prices for drinking water are rising. This increases the need for environmentally friendly technologies, and the CO2Scrub is a good example.

Back in 2009, Union installed the fist COplant with the new CO2Scrub technology. This happened in Germany at CTB (CT Biocarbonic), a joint venture project to liquefy the CO2 generated at the bioethanol facility for resale to third parties. Today, it is still considered an innovative and sustainable solution and a great business case.

However, what is the CO2Scrub, and how does it work? Søren Jensen, Process Engineer at Union Engineering and one of the developers of the technology, explains: “The CO2Scrub is essentially a gas washer where gaseous CO2 is washed with clean liquid CO2. When scrubbing the dirty CO2 gas with liquid CO2, high-boiling components and other impurities with an affiity for liquid CO2 typically oxygenate like ace-taldehyde and alcohols, and some sulphur   compounds will be absorbed by the liquid, carried away and in turn vented to the atmosphere.
The CO2Scrub is confiured as a packed column with structured packing material to minimise the amount of liquid CO2 used in the scrubbing process. Losses of liquid CO2 are minimised by reboiling, either internally in the column by means of the gas superheat or in a separate heat exchanger using heat recovered elsewhere in the CO2 plant, bringing the amount of CO2 bleed down to a level comparable with or lower than the amount lost with the water from a high-pressure water scrubber for the same application.”

Developing a new technology like the CO2Scrub is not done overnight; it is a long process, and adjustments, measurements and changes are done over and over again, until the right solution has been obtained.
Often, like in this case, external partners are also a part of the development. Søren Jensen continues: “As the amount of data on vapour liquid equilibrium (VLE) between some of the key impurities and CO2 is very limited in the academic literature, Union Engineering has researched these VLE data in cooperation with LTP (Laboratory for Thermophysical
Properties) GmbH, University of Oldenburg. In the research it was found that the data used in recognised process simulators was not correct for the temperature and pressure range commonly found in CO2 plants. The obtained
data is allowing us to predict the behaviour of the CO2Scrub column more correctly, thus avoiding undersizing the equipment. The developed VLE data is the intellectual property of Union Engineering.”

The CO2Scrub concept has found its place in the market, especially in CO2 plants based on bioethanol fermentation, where impurities like acetaldehyde and dimethyl sulphide are often found in very high concentrations. By utilising the CO2Scrub, an otherwise high water consumption can be eliminated. There is a growing interest in implementing
cleaning processes that reduce the water consumption in CO2 production. Especially in Latin American countries like Brazil, the prospects of rising water prices has boosted the interest in reducing water consumption.

Besides the considerable amounts of water saved, the technology also gives the user another huge advantage. Søren Jensen concludes: “Together with our patented NOxflsh technology used in CO2 plants extracting CO2
from fle gasses by means of amines, the CO2Scrub has allowed us to eliminate the use of potassium permanganate (PPM) in all newer plants, to great benefi for our customers. PPM – or KMnO4 – is a problematic chemical,
listed on the UN list of “chemicals used in the manufacture of narcotic drugs and explosives”, requiring a special authorisation for import and purchasing. It also requires special handling at disposal, so it is great that this
chemical is not required at a Union Engineering CO2 plant”.