Electric storm

As tissue mills try to optimise their energy consumption with sustainability as a priority, the launch by Andritz of a hood air heating system using electrical energy is very timely.

Marco Cattani and George Nowakowski report

From environmental considerations to the basic economics of running any energyintensive process, there are today many reasons for tissue mills to examine their energy strategy. Add in the uncertainty over gas supply created by the current geopolitical situation and the case for electricity becomes very compelling.

This is particularly the case in any location where wind and sun are in plentiful supply. There is a growing list of mills which source electrical energy, at least in part, from renewables. In Europe and the USA, there is tax to pay on emissions, including carbon dioxide, which provides a further incentive to use electricallypowered systems, particularly if the power is sourced from renewables rather than fossil fuels. Government subsidies on renewable energy are another factor in the equation.

In this context, Andritz has taken a wealth of knowledge regarding electrical heating, in the drying of spunbond materials for nonwovens in some of their installations and applied it to hood air systems for tissue machines. The result is the PrimeDry Hood E, which uses the same air system as gas- or steam-heated hoods, but with electric heaters replacing offering flexibility in operation gas burners or steam heaters. The result is a system capable of achieving air temperatures of between 400 and 450 deg C.

Energy efficiency boost

Compared with, for instance, gas-heated systems, PrimeDry Hood E increases energy efficiency for the hood drying system by up to 4 percent. Electrical heating is more efficient because a conventional gas burner requires heating of both the combustion air and drying air for the burner to function, while electrical heating does not require combustion air. And in theory at least, 100 percent of electrical energy is converted into thermal energy. Compared to steam-heated systems, the PrimeDry Hood E can increase production through its capability to achieve elevated temperatures.

Electrical heating offers the further advantage that no combustion residuals are emitted to the air. Overall, tissue machines can expect a reduction in carbon dioxide emissions of approximately 70 percent compared to a conventional gas-heated system. In many parts of the world, Europe and the USA included, mills pay tax on emissions to the atmosphere, so there is a clear economic argument for electric heating as well.

The potential for lower availability compared with gasheated air systems is mitigated by the use of filters with automatic cleaning in case of low temperatures, as is already implemented with steam-heated hoods.

There are two types of electric heaters available from Andritz: the Corner Type and the In-Line Type. In performance there is no difference, but each format is suited for a particular mill layout and recommended on a caseby-case basis. Electrical heating comprises the main body of the electrical resistor, a terminal box and control panel, the placement of which is flexible.

While the application of electric heating for hood air in tissue production is new, electrical heating in industrial contexts where drying is involved is not.

So, it has the benefits of being proven technology – for instance in some Andritz nonwovens installations. It also means that there are existing design solutions to manage specific situations, such as where there is the potential for seismic activity.

The electrical heater has been specifically designed with least disruptive maintenance in mind. The standard system enables easy removal of both top/bottom and laterally affixed resistors by unbolting them from the plates. Andritz proposes an even more convenient solution, in which the heating elements can be removed in bundles from the duct heater rather than having to extract the whole duct heater installation. Through a minor modification of the duct heater design, this refinement facilitates maintenance of a single heating bundle while the tissue machine continues to operate at a lower capacity, rather than being shut down completely.

A positive addition in a changing world

Electrical heating is a positive addition to Andritz ’s portfolio in a changing world. It is not going to suit every situation, but its flexibility makes it widely applicable. Renewable energy sources might not be available 24/7, but a hybrid system which can switch between gas and electric heating for hood air enables a mill to switch the fuel source, which is most suitable for prevailing climatic conditions, time of day, or even changing tariffs for gas and electricity over a 24-hour period. It is a question both of optimising energy cost and security. And if drying capacity is a limiting factor in any tissuemaking scenario, the addition of electrical heating can increase capacity.

As a new application of a tried and tested technology, there is minimal technical risk to the user. PrimeDry Hood E is equally suitable for dry-crepe tissue production as for textured or structured (TAD) tissue machines. With zero carbon dioxide emissions from combustion, there is also a benefit to the final product’s eco credentials. This will appeal to the consumer and therefore the retailer. A genuine marketing opportunity born out of technology – and based on hot air.