Worts Cooling in the Whisky Production
Heat Exchangers for Worts Cooling: Background
A Scottish world-leading company in the whisky production, has contacted SACOME to design and manufacture a worts cooler of 250 m3/h of worts.
The cooling of worts after cooking and prior to fermentation in the production of spirits, is an essential part of the process, since at high temperatures there is a decrease of the fermentation power, together with a loss of evaporated alcohol and aroma diminution.
With this in mind, our Technical Staff got involved to the maximum in the design of the worts coolers, paying special attention to the special design conditions, the high solids contents (grain, stones, straws etc.) suspended in the product to be cooled, the necessity of a precise final temperature of the worts at the exit of the cooler or the strict cleaning conditions of the heat exchanger after the production cycles. These factors make the tubular solution the most convenient.
In the following sections we talk about the special details in our design of tubular heat exchangers for the worts cooling with which the most important Scottish distilleries are working nowadays.
Corrugated Tube Heat Exchangers: The Solutions
SACOME has designed and manufactured an important number of corrugated tube heat exchangers for the most important distilleries in Scotland and, in all cases, these units are working nowadays at full capacity.
In this particular project, a cooling from 63 ºC to 20 ºC was required prior to the fermentation process in different operating conditions and the process was divided into 4 sections according to the media used to cool the product (in this case: tower cooling water, fresh water and chilled water).
The system basically works with the worts circulating by the corrugated inner tubes along 4 sections, while the different cooling media circulate by the shell tubes of the heat exchangers. It is important to comment that the design of the heat exchanger allows the connection of the shells of the sections 1, 3 and 4, with the intention to avoid the use of chilled water in those seasons when the environmental temperature allows it, which means an important economical relief.
We have also to emphasize the important advantages of using multitubular heat exchangers with corrugated inner tubes for this kind of products as the increase of turbulence as a consequence of the corrugation results in a lower fouling, an increase of the heat transfer velocity and a better homogeneity of the product at the end of the cooling process.
Worts Coolers Thermal Calculation
On the other side, our technical staff took into account the existing restriction in the outlet temperature of the fresh water as it is used in different processes and in case of do not meet this requirement the result would be a high energy loss.
In the same way, when doing the thermal calculation of the heat exchanger, we considered that this heat exchanger should be working in production cycles of 30 to 45 minutes. Every 2 or 3 cycles, we made water at 85°C run through the inner tubes for cleaning and 2 or 3 times a week we repeated the same process with a hot cleaning solution.
This tubular heat exchanger has been designed to process worts flows between 150 and 250 m3/h and to reach final temperatures of 20 to 22°C. Flows and temperature of the water also vary (for example, for fresh water between 120 and 150 m3/h with temperatures between 5°C and 19°C).
These variations involve a major difficulty in the calculation of the necessary number of modules (we checked more than 20 different operating conditions). Finally, this cooler consisted of 16 modules assembled in one frame with the objective to obtain an easy drainability (we included a system of drain valves). Other key element was the design of the expansion joints included on the shell of each module as we did a fatigue analysis of all the elements for 20 years.
To do the thermal calculations of the heat exchanger we used the last updated version of HTRI, in which association we are registered as a member. Regarding the mechanical design, we considered the BRITISH STANDARD 5500 Category 2 for the design pressure of 16 barg.
Process: basic stages in the whisky production
For the manufacture of whisky, the main distilleries prefer the new species of barley grown in Scotland, since they contain a lot of starch and are low in protein. Once the grain is dried, it is collected and stored to dry the product, before its subsequent malting .
The ground malt is placed in a circular soaking kettle, called “mash tun”. Then, it is mixed with hot water to cause the enzymes of the malt to transform the starch into a sugary liquid, (worts) which is removed from the tank to the fermentation. The waste material is called hops.
The must is pumped into large barrels (fermenters) where the yeast is added. A strong fermentation transforms the sugar into alcohol, where the resulting liquid is known as fermented must or “wash”.
The must is distilled twice in large copper stills, to produce “high wines” or “new whisky”. The first distillation in the stills causes the alcohol to evaporate and separate from the water, forming a liquid called ‘low wines’. This distillate is then transferred to the ‘low wines’ stills to produce brandy.
After distillation stage, the liquor produced or “high wine” is added water and aged in white oak vats. The duration of aging can vary, but in general it is usually between 2 and 5 years, and can reach up to 10 and 15 years.
After the aging phase, the whiskey is reduced to the desired alcohol content by the addition of soft water. The whiskey is then carefully filtered and bottled with automatic machinery in bottles that are sealed and labelled.
The worts cooler is required between the mashing and fermentation stages.
Worts Specifications for Whisky Production<
One of the key points in the design of this kind of tubular heat exchangers for worts cooling is to know the properties of the product. In this way, from our experience in a multitude of projects for the most important distilleries in the world, in SACOME we perfectly know the behavior of the worts and, in fact, we have done some rheological tests in similar projects. Besides, we also have a lot of available references and properties of other products derived from the whisky production as, for example, the “wash”.
In this sense, it is very important to remark the nature and behavior of this product as its complexity gives it special characteristics when doing the calculations. For that reason, only a company specialized in this kind of application could be able to get the optimal solution.
On the other side, the solid content makes essential to apply certain considerations in the design of the worts coolers to avoid, for example, the risk of blockage in the inner tubes.
Design of the Tubular Heat Exchanger for Worts Cooling
For this project we supplied our S-TFM-I Tubular Heat Exchanger, whose main features are as follows:
The geometry consists of a tube bundle: the worts flows in the tubeside and the service fluid (water) in the shellside. The diameter of the inner tubes is appropriate to avoid blockages.
Corrugation of tubes in the heat exchangers
In our corrugated tube heat exchangers, the inner tubes are corrugated in order to increase the turbulence of the product, thus reducing the risk of fouling and increasing the thermal efficiency.
Flanged tube sheets
The flanged tube sheets allows to easily remove the reductions to do the inspection and cleaning of the inner tubes.
Unlike other geometries (as plate heat exchangers), the maintenance costs in our tubular heat exchangers are minimum, being the gaskets the only spare parts.
Self-drainability in tubeside
An important requirement is the drainability of the product. In this way, we designed an appropriate distribution of inner tubes and we considered eccentrical reductions. Besides, we included a system of drain valves.
Thickness of inner tubes
The water circulating outside the inner tubes had some content in chlorides. So, to avoid corrosion problems, it was necessary to consider a bigger thickness of these inner tubes.
In this way, it is very important to empty each shell while doing the cleaning at high temperatures.
Non removable tube bundle
As the service fluid, in this case, is water and the client did not require a special inspection of shellside, we considered shell and tube heat exchangers with non-removable tube bundle.
Because of the high number of required units in series and the presence of different sections, we did a custom design of the required frame.
Inlet Worts Temperature
Inlet Worts Temperature
Outlet Worts Temperature
The importance of rheology in the design of any processing plant is crucial since the sizing of many of the elements composing it is very dependent on this “resistance”, also taking special relevance with food products: heat exchangers, pipes, valves, pumps, mixers, etc.
To design a heat exchanger it is necessary to have certain data, such as the process flow rate, the temperature and the physical properties of products.
Hairpin heat exchangers have a more efficient and economical design compared to a multiple pass heat exchanger when the process requires a temperature crossing between the cold and hot fluid.