Lesson 10 - Carbon Dioxide Recovery Technology
This lesson explores the technology used to recover and purify carbon dioxide (CO2), which is a co-product from brewery fermentations. Purified CO2 is used throughout the brewery to carbonate liquids and to purge air (oxygen) from vessels and packaging containers. It examines the role that fermentation and fermenter vessel operation has on the availability of CO2 for collection, as well as considering an overview of the technologies and plant involved in collecting, purifying, and liquefying CO2 for use back in the brewery.
Typical Purification Performance and Collection Efficiencies
The purpose of any CO2 recovery plant is to collect and purify CO2 to a particular purification standard appropriate for use within the brewery, or in certain situations by an external purchaser of the gas. Different standards are used around the world, but there are common concepts which are often adopted.
Collection efficiencies of CO2 plants are as much to do with operational practices as they are to do with technology selection, but general guidelines can be considered.
Purification performance
Recovered CO2 should be fit for purpose. This sounds simple, but if we reconsider the purpose or uses of CO2, inevitably they involve contact with product. General brewing considerations apply in that the recovered CO2 should be food-grade, safe for human consumption, taint and odour free, and not impair product quality. In short, recovered CO2 should comply with the raw material specification for carbon dioxide, of whatever source for our company or region. A typical specification for CO2, independent of source, is shown in the table below.
Table: Typical CO2 specification and analyses courtesy of IBD/BOC (vpm volume parts per million)
|
|
Specification |
Typical analysis |
|
Carbon dioxide |
99.95% |
99.99% |
|
Carbon monoxide |
< 10 vpm |
< 1 vpm |
|
Sulphur |
< 5 mg/L |
< 1 mg/L |
|
Moisture |
< 10 vpm |
< 10 vpm |
|
Oxygen |
< 20 vpm |
< 2 vpm |
|
Oil |
< 2 mg/L |
< 1.3 mg/L |
|
Hydrocarbons |
< 10 vpm |
< 1 vpm |
|
Ammonia |
< 1 vpm |
< 1 vpm |
|
Nitrous oxide |
< 1 vpm |
< 1 vpm |
|
Residual gases |
< 0.025% |
0.006% |
Typical collection efficiencies
Efficient operation is as much to do with the operational practices involved in running the process as it is to do with the technologies and their limitations. Further complications in this regard, are the variety of technologies available in the marketplace. However, as a general guideline, collection efficiencies fall into two groups, namely those for a recovery plant with and without a stripper unit. In such cases, typical overall collection efficiencies are 30-50% and 50-60% respectively.