This paper mill is the leader in the Spanish market and one of the top European producers of different types and weights of paper. It has a large production facility in the town of Amezketa (Guipúzcoa, Spain), with a total production capacity of 115,000 tons of paper per year. Until 2009 it had a combined heat and prower plant consisting of a gas turbine and a gas engine for a total of 9MW of electricity generation to supply its plant consumption. However, due to its need for growth in terms of production with the introduction of new machinery and therefore new consumption, the existing CHP plant was insufficient.

After analyzing the different alternatives, a project for the complete revamp of the cogeneration plant was proposed, increasing its electrical and thermal generation capacity to 14 MW. The cogeneration would have a combined cycle including gas turbine, heat recovery boiler and steam turbine. AITESA was entrusted with the engineering, design, manufacture, assembly and commissioning of the heat recovery boiler. The recovery boiler feeds steam to the steam turbine and also supplies steam to the production process. Therefore, it generates steam at two pressure levels, high pressure, superheated steam at 40 bar(g) and 400ºC in the natural circulation section, and low pressure, saturated steam at 7 bar(g) following the previous one, in the forced circulation section. To adapt the steam generation to the steam turbine and plant steam demand, the boiler incorporates an afterburner, which permits a generation of 23.5 ton/h of high pressure steam and 2.1 ton/h of low pressure steam. In addition to the supply and assembly of the static mechanical elements and pressure apparatus (boiler tube banks, casing, boilers, structural elements and accesses), AITESA provided the instrumentation for the control and safe operation of the boiler. It also supplied the control and power panels to control the electrical consumers of the system (feed pumps, recirculation pumps, afterburner ramp fans). All these elements required integration within the DCS of the plant, in order to coordinate with the rest of the components in the different operating modes of the combined cycle. AITESA completed the assembly of the complete boiler in 2010 with plant start up in May 2011.

The incorporation of the recovery boiler, together with the rest of the elements of this new combined cycle, has allowed this paper mill to increase its capacity and reduce its production costs, thus increasing its competitiveness in the market.