Lesson 10 - Carbon Dioxide Recovery Technology

Before looking at the process of CO₂ production and recovery in detail, we should first consider what is involved in CO₂ recovery at a high level. There are three important technological aspects which we need to be clear about:

• Fermentation: the biochemical reaction which produces carbon dioxide (as well as ethanol and flavour and aroma compounds).

• Fermenter: the vessels within which fermentation takes place.

• Fermenter block: a group of fermenters which cumulatively collect and supply carbon dioxide to the recovery plant.

These three technological aspects are shown schematically below.

Figure: The differentiation of fermentation, fermenters, and a fermenter block

It may be unclear why we have given emphasis to fermentation, a fermenter, and a fermenter block. What we are trying to draw attention to is the following:

• A fermentation, as a biochemical reaction, produces carbon dioxide which is released from the fermenting wort liquid volume. Representative reaction equations for fermentation are well understood and available. These allow us to quantify the amounts of CO₂ produced during fermentation (we will look at this in a later section).

• A fermenter emits CO₂ once the gas has been released from the fermentation (literally from the fermenting wort), and once it mixes and displaces the gaseous headspace of the fermenter. This headspace is initially full of air following cleaning of the fermenter before filling. The initial gas emitted from the fermenter is very rich in air and lean in CO₂, and as the fermentation progresses, the emitted gas becomes richer in CO₂.

• A fermenter block consists of several or often all fermenters in the brewery, where the CO₂ gas emitted from all fermenters is collected in a common pipe and fed to the CO₂ recovery plant. The consequence of collecting gases from all fermenters in a common pipe is that the gases mix together, both lean and rich in CO₂.

The mass flow rate of collected gases from the fermenter block is the accumulation of all fermentation gases from all fermenters.

• Fermentation is the biochemical process which produces CO₂ (and other useful products).

• A fermenter is a vessel within which fermentation takes place. It emits a mixture of fermentation gas and air, which increases in CO₂ richness as fermentation proceeds.

• A fermenter block is a group of fermenters which cumulatively collect and supply carbon dioxide to the recovery plant. The concentration of CO₂ and flow rate is the accumulation of all fermentation gases from all fermenters.

Keeping these three distinct but related concepts at the front of our minds, let us now look at how a brewer can quantify the amount of carbon dioxide that fermentation, a fermenter, and a fermenter block can produce.