CO2 capture in a small brewery – a case study

The UK’s small brewers (those producing below 100,000 HL/yr[1]) account for the production of approximately 215 million litres of beer, at an average ABV of 4.6% (3.65% ABW)[2]. Taking into account fermentation vessel (FV) losses (10%), stoichiometry[3] informs us that the total amount of CO₂ produced by this fermentation is: 

1.1 x 3.65% x 0.9565 x 215 = 8.26 million kgs, or 8,260 metric tonnes (t), or 0.038 kg/l. 

Until very recently, all of this was vented to the atmosphere.               

Of this beer, around 100 million litres are packaged flat, into cask[4]. Therefore, 115 million litres of small brewery beer is carbonated, and, whilst some of this will undoubtably be carbonated via a spunded fermentation, the vast majority will rely on liquid CO₂ purchased on the wholesale market, not only to carbonate the beer, but also to back pressure vessels and fillers in order to prevent that carbonation from escaping. 

Bottling, canning and kegging in small brewery packaging facilities typically uses up to 0.05 kg per litre to carbonate the beer and run the filling machines[5]. Therefore, as an industry, we are on the one hand releasing 8,260 t of CO₂ into the atmosphere as a result of fermentation, and, on the other hand, purchasing 5,750 t of CO₂ from the wholesale market to put back into the beer. In the days of plenty, marrying these two CO₂ streams up (one out, the other in) via technology wasn’t considered worth the hassle, despite the engineering being already fully available (albeit in a macro form). Recent price rises in wholesale liquid CO₂ (and a couple of industry-wide droughts of the stuff) have changed the dynamic; two firms have entered the market, seeking to provide a solution that matches up this supply with the demand, by capturing the evolved CO₂, rendering it fit for use and liquidising it for storage and transport. Earthly Labs, based in the US, have developed a CO₂ recovery unit for craft brewers above the 15k hl/yr scale, and have some units operational in the US. Dalum Beverage Engineering from Denmark have developed a unit suitable for brewers producing 5k+ hl/yr scale, of which there are two already operational in Denmark, a third recently installed at GADDS’ The Ramsgate Brewery in the UK, with more units on their way to the Faro Islands, Norway, Bristol and beyond. This paper is an attempt to explain the principles and reality of capturing fermentation-evolved CO₂ from a small brewery, and transporting it to a craft drink packager for reuse, in place of wholesale gas.

 

The installed system consists of collection pipework, a foam trap, the capture unit and transport/storage vessels.

 

Collection

CO₂ is collected from closed FVs via the CIP arm. Following the lag phase, active fermentation clears the vessel headspace gas (air) and the O₂ content is monitored via a handheld unit held at the CIP arm. Once below 0.6%, the collection can begin. The CIP arm is connected, via a 1-inch braided hose, to a manifold leading to a 1-inch collection main, a PRV (in case of unit failure) and a foam trap. The system is designed to operate at 0.25 bar, a low enough pressure not to trouble the yeast or flavour profile of the beer.

 

O₂ monitoring

From the foam trap, the CO₂ enters the capture unit and is now monitored for O₂ content by the unit. Should the O₂ content stray above 0.6%, the gas is vented until O₂ levels lower. In reality, oxygen levels in evolved fermentation gas fall to below 0.6% within a few hours and don’t increase thereafter.

 

Low pressure scrubber

The gas enters the base of a 3m tall, narrow cylinder filled with surface area busting stainless steel pall rings. Cold water is trickled down the column as the gas makes its way up it. Here, alcohols, esters and other impurities are picked up by the water (thereby separating them from the gas) and the resultant effluent is collected as a ‘grey’ water supply.

 

Compression

On leaving this column, the clean gas runs through a solids filter and onto a 3-stage compression process, with intermediate cooling and water removal stages. The Dalum designed, oil-free, variable speed, single stroke, 3-stage compressor is right at the heart of the unit. Gas is compressed to 35 - 45 bar in the multi-cylinder piston chamber, regulated to 60°C, and the moisture removed is collected as grey water. Between stages 2 and 3, the gas passes through a high-pressure sulphur scrubber.

 

Dehydration

The dry gas, now at ambient temperature and high pressure, passes through a column containing inert aluminium oxide desiccant, for super drying. The degree of dryness of a gas can be expressed in terms of the dew point – the temperature at which, under constant pressure, the gas has 100% humidity. The lower the dew point, the drier the gas. On exiting the dehydration columns, the CO₂ has a dew point typically of -60°C.

 

Rectification/liquefaction

At 35+ bar, the super dry gas now only requires cooling to 3 or 4 °C to liquify and enters a Dalum designed glycol cooled condenser, and on to a reboiler. Constant boiling releases O₂ molecules from the liquid phase CO₂, which migrate back through the condenser and are vented off periodically. Purified, liquid CO₂ collects in a small tank at the end of the system and is pushed into 240 litre transport vessels.

 

Collection, storage and transportation

The brewhouse at GADDS’ produces 26 hl of wort per brew, fermented in either single or double batches under a top pressure of 0.25 bar. After a lag phase of around 8 hours, a single fermentation will evolve gas with an oxygen content below 0.5% and at a rate of 1.5kg/hr for approximately 48 hours. A handheld O₂ monitor lets the brewers know when to hook up the fermentation to the collection system (generally 16 hours from yeast pitching). Some CO₂ is lost through the initial stage of fermentation, due to high O₂ content, and some remains in the beer at the end. With good management, 75% yields have been achieved, with an oxygen content of <6 ppb, measured with an Orbisphere (wholesale liquid CO₂ at the bottling site measures 20 ppb O₂). A burette is used to demonstrate purity >99.99%.

 

The vacuum insulated transport tanks, mounted on a skids with casters, and equipped with internal vaporisers, are used to store and transport the collected gas to the bottling site. Under the ‘small limit’ threshold of 1000kg for CO₂, these can be transported legally without any onerous specialist safety equipment.

Once off-loaded at the bottling site the tanks are connected to the CO₂ systems simply via a standard 3/8-inch line and a secondary regulator. Due to the high quality, this recovered gas is reserved for carbonation rather than providing back-pressure in vessels and fillers.

 

Review

This compact unit has a footprint the size of a pallet, but delivers a game-changing service to the small brewer. The engineering is inspired, and the quality of the build first class. This isn’t a noisy machine; it sits and rumbles quietly, hissing every now and then to let you know it’s still working. And though reliability is excellent, you won’t get the best out of the unit unless you make the effort to engage with the principles, learn to drive it, and flex your collection system to suit. This is all well within the reach of the practical brewer, and there’s a handy remote management system that records and rewards your efforts. In the interests of balance, I’m desperately trying to find something negative to say about this, but I can’t. In my opinion, as an engineer turned brewer, this is awesome.

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[1] This report is primarily about technology that has recently become available to the smaller brewers – it has been available to those brewers above 100k HL for some years.

[2] SIBA Members Survey 2021

[3] Balling, Carl. J. N., Die Bierbrauerei. Verlag von Friedrich Temski: Prague, CHZ, 1865. 

[4] SIBA Members Survey 2021

[5] South East Bottling internal audit.