CO2 CAPTURE

Introduction

 

With this chemical capture system, the flue or exhaust gases are led through an absorption column where a chemical solution, the “solvent” will bind with the CO2 molecules. The chemical captured CO2 in the solvent, so called “rich solvent” is lead to a stripper column. In the desorption / stripper column, the CO2 is regenerated from the solvent and obtained in a purity of 99%, and if required, in food grade quality. The CO2 can e.g.,  be distributed into a greenhouse as fertilizer.

The gas treating part of the process (Quench and CO2 capture plant) have been designed with the Procede Process Simulator. This is a rate based simulator specific developed for the development of gas treating processes, All relevant properties of the Bilisol® solvent have been measured and incorporated in the process simulator. The CO2 capture plant built at Twence is a smaller version of the Bilisol® CO2 capture plant compared to the one operating in Delta (British Colombia). Both plants are designed by the  Procede Group BV. 

At the plant in Delta the CO2 is captured from a flue gas stream coming from a wood burner and the CO2 is directly used as fertilizer to growing fruits and vegetable.

The flue gas captured from the Waste-To-Energy (WTE) plant of Twence by the Bilisol-process is used for the production of sodium bicarbonate. The latter process is a new innovative process developed by Procede, the CO2 produced by Bilisol is converted in an innovative new reactor configuration from sodium carbonate directly to sodium bicarbonate (SBC). The produced SBC slurry will directly be used at the WTE plant to purify the flue gas stream, before it is released to atmosphere.

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Nitros- Amines

 

The solvent is a special developed and patented organic solution which is in no way harmful for plants and / or environment. In contradiction to the standard Amine processes where a combination with NOx can create Nitrosamines that are harmful for the people, working in the closed environment, such as the greenhouse, this solvent is purely based on organics.

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Dioxines

 

“Based on the generalized structure formula of dioxins it is not likely to expect that the compounds will react with the CO2 selective solvent. Therefore the only option left is the physical absorption of dioxins in the solvent. The solubility of the dioxin has not been measured for our solvent but it is more than reasonable to assume that the solubility in the absorption solvent is lower than that in water. Moreover, the transfer of dioxins from the gas phase to the solvent is a physical process and is therefore slow compared to the chemical absorption of CO2. As there is no data available on a/o transport characteristics  it is difficult to give exact numbers how much dioxin will be present in the CO2. Based on our experience on other “inert” compounds like CO or N2 it is can be stated that the concentration of these inert compounds in the CO2 produced are much lower than the concentrations in the flue gas”.

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The solvent

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The solvent was developed in the past years in several theoretical and practical studies, performed by Procede Group, the Universities of Groningen and Twente, and in cooperation with a client in Canada where we have a full scale system in operation on a biomass (wood chips) fired system, providing CO2  for a greenhouse facility which also is used as test facility for improvements on the systems (energetic) performance.

CO2 rich flue gases enter the absorption column at the bottom and are contacted counter-currently with the solvent. The CO2 rich solvent is heated in the main heat exchanger by the CO2 lean solvent from the bottom of the stripper column (via the solvent storage tank). The heated CO2 rich solvent enters the stripper column at the top. In the stripper column CO2 (and water vapor) are released from the solvent. The CO2 lean solvent from the stripper column is cooled in the main heat exchanger with cold, CO2 rich solvent and is further cooled before it is sent back to the top of the absorption column.

Gas, which is released in the stripper column, is cooled to condense the water.The condensed water is sent back to the absorption column (not shown). The required heat for stripping CO2 out of the solvent is provided to the stripper column by means of a forced reboiler. Heat required for driving the CO2 absorption process is supplied by the biomass boiler. Condenser and cooler heat is recovered and will typically be transferred to the heat storage buffer tanks. Overall heat integration is high and heat usage is maximized resulting in an energy friendly process.

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                                                 Process flow diagram Bilisol®

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Advantages

 

The process has the following major advantages compared to a conventional CO2 capture process:

• During night time, when only heat and no CO2 is required in the greenhouse, the stripper column will not be operational. As the solvent is stable at high CO2 liquid loadings, the absorbed CO2 is stored overnight in the storage tank, leading to a smaller absorber design and cost savings.
   

• In the process, the captured CO2 is used as a greenhouse gas and needs to be very pure. The very low vapor pressure of the special developed solvent, reduces the overhead losses in the absorption- and stripper column. The low vapor pressure will increase the quality of the greenhouse gas, i.e. the chemical impurities in the greenhouse gas will be negligible.
   

• The solvent is specifically developed for greenhouse applications possessing the important properties; fast reaction kinetics, good CO2 capacity, no vapor pressure and low degradation rate.
   

• The solvent is not an amine. Amines in combination with NOx concentrations (typical in combustion exhaust gases) create Nitrosamines which are carcinogen, see above.