Who hasn't been there: too cold to brew outside, chased out of the kitchen. No garage? OK, down to the cellar we go. Halfway through the boil you notice water dripping from the ceiling. It's normal to boil off 3-6 Liters of water during a 60-90 minute batch. What should one do with all that steam?
A special thanks to "Brundog" from the homebrewtalk.com Forum, who kicked off this idea and really got the ball rolling.
I'm pretty lucky to have my own space in the cellar to brew, but since day 1 I've been fighting the unavoidable steam problem. To be honest, I haven't satisfactorily solved the problem yet. My solution until now was pretty simple: put a big fan in the window facing out, and open another window for cross ventilation. Very loud, very cold, very inefficient!
If you've faced the same problem, you've probably already looked at other solutions such as a domed kettle cover with exhaust vent to the outside, or installing a really big exhaust hood over your kettle. Maybe you've ruled out those other options like I have. That's why I've recently looked into another option: the steam condenser.
The basic idea behind the steam condenser
The idea is pretty simple. We route the steam into a mixing chamber into which we inject cold water in a fine mist. The cold misted water absorbs heat from the steam and the steam undergoes a phase change back to liquid water. We achieve a large volume reduction in the condensation of the steam vapor to water, and create a small vacuum, pulling more steam from the kettle. The now heated water and condensed steam flow out the bottom of the mixing chamber as (very) hot water.
How much cooling water do we need?
That was the first concern I had when researching this idea. just how much cooling water will we need? Luckily we can get an estimate using a few simple calculations. Now it's been a long time since I had physics and thermodynamics, so please forgive me in advance if I've got some of the terminology wrong!
From thermodynamics we know how much energy it takes to transform water to steam (vaporisation heat). we also know the energy capacity of the water, with which we will cool the steam (the specific heat of water).
I will assume an input water temperature of 10C and a boil-off rate of 4 l/hr. The boil-off rate will depend on your particular brewing setup (mostly kettle size and heat source), but I think this is a good starting point.
|Cooling water temperature||10C|
|Boil-off rate (system dependent)||4 L/h (kg/h)|
|Specific heat capacity of water||4,184 kJ/(kg·C)|
|Vaporisation heat of water||2.260 kJ/Kg|
|Temperature difference between boiling and cool water temp||100C - 10C = 90C|
|Theoretically available cooling capacity||90C * 4,184 kJ/(kg·C) = 376.56 kJ/kg|
|Energy consumption to produce the steam during boil||2260 kJ/kG * 4 kg/h = 9040 kJ/h|
|Required cooling water||(9040 kJ/h) / (376.56 kJ/kg) = 24 kg/h|
For this example we require 24 l/hr of cooling water. This was the starting point for my design and testing purposes.
Enough theory already!
How do things look in practice? The idea of using a steam condenser for brewing is not a new idea. There is already a version for larger breweries available and it has been fairly well discussed in the German homebrew forums as well as the main American Forum. And the first commercial steam condensers for the homebrew market are already available in the U.S.
Reports in the homebrewtalk form indicate that users have had to reduce their heat input when covering their kettles to prevent a boil over. Already more than a few users have had to reduce their heating elements by up to 50%. As a result they also report reduced boil-off rates, that remain however above the generally accepted industry standard (if there is such a thing) of a minimum 4-5% boil off rate. I can live with that.
And what about DMS? I mean that's one of the main reasons we want to get the steam out of the kettle in the first place. Does the steam condenser work as well as an open kettle? I have yet to find any lab measurements in this regard, but again the experience of fellow home brewers look encouraging. And why not? After all, we are still pulling the steam out of the kettle, and with it the dreaded DMS.
Status of the Prototype
Armed with the information from the home brewing forums and the above mentioned calculations, I have begun developing my own product for sale in the EU. My goal is to build a steam condenser that:
- maximizes the cooling capacity
- minimizes water consumption
- can be retrofitted into existing systems
- and is made from high quality materials.
In order to maximize efficiency (as it relates to the cooling capacity and water consumption), we need to ensure the best conditions possible for heat transfer between the steam and the cooling water. To achieve this, the cooling water nozzle should provide the finest spray possible: smaller droplet size creates more surface area for heat exchange. There should also be enough time for the interaction of steam and cooling water before the cooling water hits the inside wall of the condensing unit, thus condensing into larger droplets itself thus losing most of its cooling capacity.
A few factors that we can change are the chamber diameter and the type and form of the spray nozzle. To test the former, I made 4 prototype condensers with different inside diameters: 40 mm, 50 mm, 65 mm, and 80 mm. In the area of spray nozzles, I looked into several larger German and Japanese manufacturers and found several different full cone and hollow cone axial spray nozzles, that meet the required flow rate while minimizing the mean droplet diameter.
I am also testing the difference in performance when mounting the condenser in the kettle lid vs. the kettle wall; the use of a gasket between the lid and the kettle; and the diameter of the steam input to the condenser.
It could be a little while before I have a product that is ready for sale.
[ Update: the steam condenser is now available in the shop! ]
Until now, I have only been performing water tests. But the results look very promising. Until now I have found that enlarging the diameter of the steam condenser above 50 mm ID does not have a large impact on performance, at least in the 40-60 L kettle size range.
Because my last keg of beer is dry, I plan to perform some full brew tests very soon.
Do you already have and use a steam condenser on your brew kettle? Are you interested in getting one? I would be happy to hear your feedback in the comments below!