For food manufacturers dealing with viscous products, the design and specification of appropriate pipework is crucial. Whilst jacketed pipework is familiar territory, what are the latest solutions available to minimise seepage and optimise temperature control? Stephen Forrester, MD of adi Process Pipework, provides his analysis.
Viscosity plays a key role in any industrial process where liquid is involved, but it is particularly important in the food & beverage sector. For example, high volumes of liquids, ranging in viscosity from aqueous to pasty, must be carefully pumped through pipelines to ensure the quality of the product is maintained.
Process pipework systems carrying viscous products must be sized correctly dependent upon the viscosity and operating pressure that needs to be achieved, to provide the appropriate flow rates to service plant items such as temperers and depositors.
However, problems arise when fluctuations in temperature cause the viscosity or state of the liquid to change. Often, liquids carried in pipelines are much hotter than ambient temperature and, as such, experience heat losses if temperature control measures are not implemented. For example, concentrated sugar slurries used in confectionary production often require preventative measures to stop the formation of sugar crystals which can adversely affect seal performance in the pumps and valves.
One of the most widely-used solutions in the industry is jacketed pipework. This involves is passed through to either heat or cool the liquid in the inner tube. This maintains a consistent temperature of the medium that is being transferred to ensure that a constant flow rate is achieved.While the concept of jacketed pipework is straightforward, and is used successfully in thousands of different process applications, there are several recent innovations which provide superior temperature control, reliability and efficiency. These include:
The triple jacket system uses 316 stainless steel on the inner skin where the product is in contact with the pipe. There is a fully welded 304 stainless steel jacket over the tube, and fittings with an inlet and outlet connection which allow the flow of hot water through the jacket sections at a controlled temperature to heat the product. The triple jacketed system then has a further fully welded jacket which is filled with suitable insulation sections before welding.
This design drives the heat inward, towards the product, which makes it more effective and efficient than conventional jacketing.
This also means that the heat does not escape into the area and raise the ambient temperature of the building, therefore reducing the need for air conditioning. Whilst the initial cost outlay is higher than normal jacketing, the long-term energy savings provide an attractive return on investment.adi developed this system for a chocolate production installation in Poland in 2008 but this has since been rolled out across other manufacturers and contractors.
Fats in certain products often seep out of the flanged gaskets normally used such as nitrile and gortex. However, captured O-ring gasket systems are proven to prevent the seepage that often takes place.
This is where a normal O-Ring, usually made of either of either Buna®-N or Fluorocarbon, is held between two aluminium retaining rings to form a vacuum seal. This is a more effective sealant than a flanged gasket as it provides a food hygiene grade encapsulated seal that has proven to be far more effective in the long-term prevention of degradation or seepage when in contact with viscous products such as sugar syrup, glycol or chocolate.
Long radius bends
Long radius bends present a challenge to some manufacturers, as pre-fabricated jackets are not always available in the correct dimensions. In these instances, a bespoke solution is the best choice, however this can be costly and involve a number of different parties.
Service providers such as us may also have the facilities to manufacture highly customised products which allow to incorporate long radius bends. For example, we can use long radius bends of up to three diameters for the inner bends and have also used triple jackets for pigging systems.
The primary alternative to jacketed systems is trace heating. Trace heating involves running an electrical heating element – known as ‘heat tape’ - along the length of a pipe to maintain the temperature of the material within. The pipe must then be covered with a layer of thermal insulation to prevent heat loss and increase energy efficiency.
With its useful thermal properties, such as the ability to transport heat over long distances while giving up its heat at a constant rate, steam offers a useful alternative to electrical heat tape in trace heating applications. Steam tracers can often use excess process steam that would otherwise go to waste, making them a highly efficient option. And in the absence of a live electrical current, steam tracing is inherently safe and suitable for use in all zones.
However, the main issue with any trace heating system is the inconsistency of temperature it provides. Typical trace heating systems will generate hot spots that can bake off the product which are then compounded by cold spots in other locations. While a self- regulating tracer cable can adjust its watt output at any point along the entire length of the heater circuit, helping to prevent hot or cold spots, a triple jacketed system will still offer superior temperature consistency.
As an example, we recently completed an upgrade of a trace heating system to jacketed pipework for a well-known UK biscuit manufacturer. The work involved replacing the old and expensive to use trace heated copper pipework with new stainless steel jacketed pipes and filters. Totalling 150 metres in length, the pipework feeds the syrup from the holding tanks to eight mixer facilities. The pipes were manufactured in 3m lengths at our manufacturing facility in Somerset and transported to site for installation.S
Since these production systems are in operation 24/7, it was crucial that there were no interruptions to the process and no bacterial issues. Therefore, all the pipework was both pressure and swab tested, with every weld undertaken by a specialist coded welder.
The result was significant energy savings for the manufacturer. A costly process, which used a significant amount of electricity, was replaced with four heaters to provide a flow of hot water around the jacked pipework system.
The second alternative to jacketed pipework is ‘limpet jackets’ or ‘limpet coils’. Limpet jackets offer a relatively inexpensive temperature control solution; however, as the system is not in close proximity to the product, heat transfer is inconsistent. As with trace heating, insulation is also required with limpet jackets to retain heat which is an added expense.
An issue affecting both limpet jackets and trace heating systems is the inability to fully weld the insulation jackets required. Therefore, they are far more susceptible to damage, particularly when used in rugged industrial environments. Damaged insulation does not retain heat properly, meaning the product within the pipework is not maintained at the correct temperature.