Volume 25, number 1, June 2011

Energy Efficiency and Productivity: A Winning Combination for Technocell Inc.

Technocell Inc., a subsidiary of the German Felix Schoeller Group, is a manufacturer of decor paper in Drummondville. The plant employs 120 people and every year produces 30,000 tonnes of paper, principally used in making laminated products. Firmly committed to improving its competitiveness and to reducing its ecological footprint, in 2006, the company conducted a complete analysis of its energy consumption and drew up a list of projects and initiatives designed to achieve its objectives. The project to recover energy from the boilers’ combustion gases began in 2007 and further steps toward energy optimization have been taken since then.

Improving boiler performance
The boiler room is a huge energy guzzler. It consists of two thermal fluid boilers, 1,500 HP each, and a 600 HP steam boiler. Fitted with an economizer, the latter replaced a steam generator that was judged obsolete and inefficient. The two thermal fluid boilers exhaust their gases through a common chimney.

An indirect contact condensing economizer was installed to recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. In winter, the temperature of the gases can thus be lowered from 200°C to 10°C, while preheating the process water from 8°C to 80°C. On average over the year, boiler combustion efficiency has risen from 80.9% to more than 95%. The efficiency of heat produced from either thermal fluid or steam is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency.

Indirect contact condensing economizer
The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends of the excess air. Natural gas has different combustion efficiency curves, linked to the temperature of the gases and the excess air. For example, if the gases are chilled to 38°C and there is 15% excess air, then the efficiency will be 94%. The indirect contact condensing economiser can thus recover the sensible and latent heat in the steam condensate contained in the flue gases for the process.

The economizer is made of an aluminum and stainless steel alloy. The gases pass through the cylinder and the water through the finned tubes. Figure 1 shows a simplified flow diagram of the combustion products as well as the process water, which also serves to heat the make-up water for the steam boiler. Since the Technocell plant operates day and night, the economizer has a recovery potential of 8 MMBtu/hr and can maintain an annual average of 100 MMBtu per day. It condenses about 11% of the water contained in the gases. A project with a payback period of 1.39 years, with subsidies, can save about 1,150,000 m3 of natural gas per year.

Figure 1 – Simplified flow diagram

Other projects for even more efficiency

With the help of an external firm, Technocell carried out a mass and energy study of its dryer section. The results of this study clearly demonstrated the optimization potential of the dryer section’s equipment and operating methods. A control strategy was developed with PremiAir to ensure an optimal rate of humidity in the dryer section through, in particular, efficient ventilation management. The annual savings are 680 MWh and 600,000 m3 of natural gas. Also, the higher humidity in the exhausted air increases the efficiency of the exchangers on the extractor chimneys, which leads to additional natural gas savings.

Assessment of measures and future prospects
Besides the implementation of the indirect contact economizer and the optimization of the dryer hood, a reduction in fresh air consumption was also achieved. The consumption of natural gas was reduced by almost 30%, while supporting an increase in production of almost 18%. Figure 2 illustrates the reduction in natural gas consumption per tonne of decor paper produced. The energy savings have also led to a reduction of 4,200 tonnes per year in GHGs emissions. Several other projects are under way to reduce the plant’s energy consumption even more. Technocell has definitely shown that it is possible – even necessary – to develop sustainable manufacturing activities while improving its competitiveness on the world market.

Figure 2 – Reduction in energy consumption per tonne of product

Marie-Joëlle Lainé, Eng.

With the collaboration of:
Richard Cadrin, Eng.