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.
Point of Reflection – Reconvene
Welcome back! So, what were your thoughts?
Let us consider the three approaches separately:
1. Timer
Advantages – simple; no instrumentation required (such as gas analysers); only requires a clock (as in a wristwatch or a PLC timer).
Disadvantages – no explicit measurement of oxygen concentration so variances cannot be accounted for (e.g. variable quantities of oxygen in the raw gas due to variations in fermentation rates, and differing headspace volumes due to differing brew lengths or numbers of brews collected).
This method can be combined with a manual or portable CO2 purity measurement from an individual bung line at the scheduled time of changing from vent to collect. If the purity is within specification, the fermenter can be switched to collect. If not, it is good practice to wait approximately eight hours and repeat the process.
2. Bung line oxygen measurement
Advantages – an explicit measurement of the oxygen content of the raw gas leaving the fermenter; can accommodate differences in oxygen concentration (e.g. part filled fermenters, differing fermentation rates of differing brands, etc.).
Disadvantages – capital and maintenance cost of additional instrumentation (one per fermenter bung line if fixed-in-place); alternatively, additional measurements of each tank which can be time-consuming; does not measure the oxygen concentration of the cumulative gas in the collection main being supplied to the recovery plant.
3. Collection main oxygen measurement
Advantages – only requires one measurement point and/or piece of instrumentation per collection main; explicit measurement of the oxygen content of raw gas being presented to the recovery plant.
Disadvantages – cost of additional instrumentation (one per collection main). Also, there is no indication of gas purity by tank, so if the overall purity becomes unacceptable, it is necessary to identify the contributing tank (by manual or mobile measurement) and corrective action must be taken (e.g. take the faulty tank off collect and reconnect in approximately eight hours (with or without retest).
We have now discussed the production of CO2 and how to conduct preliminary purification of the raw gas from the fermenter by venting it to the atmosphere. It is, therefore, time to consider the process that we supply the CO2 to when we turn a fermenter on to collection. We will now look at the recovery plant itself.