PEi Report – Cogeneration to Trigeneration: Trigeneration weaves it magic in Spain

The major synthetic fibre plant of Inquitex SA has attained industry-leading standards of operational efficiency and productivity as the result of a continuing modernization programme centred on an upgrade of the cogeneration system at the heart of its manufacturing process.

Inquitex, which was formed in 1952 and is the only plant of its type in the Basque country, draws on the river’s high-quality water for its synthetic fibre production. Its output comprises polyamide fibre, which is used in the textile industry and in non-woven fabric for hygiene and cleaning products, polyester fibre for the automobile industry and hygiene markets, and PET laminate for a wide range of applications in the food, printing, cosmetic and pharmaceutical sectors. The company is also making major advances in imitation natural and animal fabrics representing silk, mohair, angora and fur.

Inquitex’ trigeneration plant is powered by a pair of 12 cylinder Rolls-Royce B3:40 gas engines
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Two-thirds of the plant’s output goes for export, with its main markets including the UK, France and Germany. Inquitex is also aiming to expand in eastern European markets, in particular the Czech Republic.

Against this competitive international background the company has gained a high reputation for service, quality and flexibility in the development of new products. Its ability to respond smartly to customers’ needs is strengthened by a pilot production line on which, for example, new colours can be introduced quickly to the product range.

“To compete successfully in Europe you have to offer added value,” says Miguel Angel Martin, managing director of Inquitex. “To ensure this, Inquitex complies with the strictest regulations with respect to quality and environmental care, while adhering to the philosophy of quick and flexible customer service.”

Securing power supply

To put this philosophy into practice Inquitex relies on a newly installed on-site combined heat, power and cooling plant to ensure efficient, safe and environmental-friendly supplies of electricity for heating and chilling.

Security of supply is crucial to the Inquitex manufacturing process, which demands a huge amount of thermal energy in the form of saturated steam and hot water. This process continues throughout the year with just two scheduled annual shutdowns, representing a total of 325 days (or 7800 working-hours) of operation for the factory. Inquitex took the decision to invest in its own natural gas fuelled cogeneration plant in the mid-1990s, when the first such facilities were being built in Spain.

“In this industry transient voltage or current micro-cuts can badly affect the quality of the fibre,” adds Martin. “Having our own power source is the only way to protect ourselves from this potential problem.”

“We chose a new Rolls-Royce powered system, having seen the benefits of a similar facility in use at Viscofan, the first industrial plant in Spain to become equipped with Rolls-Royce units. What further convinced us was a report by CADEM, the Basque government agency for energy development, that recommended these engines.”

This initial 1995 development by Inquitex was based on a single Rolls-Royce K-series gas engine, a KVGS of 3 MW, the performance of which exceeded expectations. A second engine was brought in three years later.

Upgrading to trigeneration

By the mid-2000s both engines were still operating reliably, with totals of 84 000 and 61 000 running-hours, respectively. However, in its ongoing drive to increase efficiency and cost-effectiveness Inquitex elected to invest in a major new trigeneration plant and selected for it the Rolls-Royce B35:40V AG unit.

This medium-speed, spark-ignited lean-burn series of engines is designed to produce up to 8.5 MW of electrical power. The B-series engine’s design is driven by stringent requirements for lower exhaust emissions and maximum electrical and heat recovery efficiency, linked with extreme reliability. Key features of the B-series power units are their enlarged cylinder volume and optimized combustion technology, both aimed at maximizing performance without compromising reliability.

At Inquitex two of these natural gas-fuelled power generators operate at a maximum power capability of 4845 kWe at terminals and 259 kWe of rated power at the condensation steam turbine. They run at 750 rpm with exhaust gas flow of 28 300 kg/h, maintaining a high-temperature circuit flow of 108 000 cubic metres per hour at 90 à‚°C and 79 à‚°C, with a low-temperature circuit flow of 120 000 cubic metres per hour at temperatures of 54.2 à‚°C and 26 à‚°C. The engines are started by injecting compressed air into the cylinders at 30 bars.

Steam generation

Hot water supplied to the factory is either used directly in the production process or in a 0.5 litre CoP absorption cooling machine to produce required amounts of cold water.

Total demand for process hot water at the Inquitex plant today has grown to some 8.8 million th LHV/year. This is produced in an operating regime that involves 6552 hours per year of the steam turbine in operation, 6552 hours per year with both engines running and 1248 hours per year with one engine undergoing maintenance.

Exhaust gases from the engines heat a combined boiler fitted with an economiser to generate steam
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Exhaust gases from the engines at a temperature of 415 à‚°C heat a combined boiler fitted with an economizer to generate steam, with a maximum recovery capacity of 6500 kg/h at 9.5 bar and conventional capacity of 6000 kg/h at 9.5 bar. A gas compensator is fitted at the exhaust manifold of each Rolls-Royce engine and the gases are led from here to the corresponding distribution valve to be sent to the steam boiler and/or into the air through bypass stacks. A silencer is also installed between the exhaust gas outlet and the distribution valve to achieve a noise attenuation of 35 dB(A). Steam generated in this boiler is sent either to the plant’s production process or to the condensation steam turbine to generate electricity to meet an annual demand of 70 760 MWh/year.

Buckets of hot water

Meanwhile energy in the high-temperature cooling circuit of the power generators is recovered in the factory system, feeding hot water to the process and the absorption machine. Surplus energy in the engines’ high-temperature cooling circuit is dissipated through an air-cooler with 2100 kW of cooling power. Its built-in design margin of 30 per cent is more than enough to dissipate all the thermal energy contained in the engines’ high-temperature cooling circuits. Heat from the power generators’ low-temperature cooling circuit is dissipated through cooling towers at the factory.

Powering up the process

Electricity is produced by the alternators of the cogeneration modules at a rated generation voltage of 6.3 kV. This voltage is increased through an interconnected step-up transformer to 132 kV for the Inquitex power system. Electricity produced by the cogeneration plant powers all Inquitex facilities and the auxiliary requirements of the cogeneration facility itself. Surplus electricity is sold to the grid.

The Inquitex plant uses a horizontal combined shell and tube boiler for production of saturated steam and a Dresser-Rand turbine with inlet steam conditions of 175 à‚°C (saturated) and 3700 kg/h, while counter-pressure at the exhaust is 0.14 bar. The turbine is coupled to a synchronous triple-phased alternator. A condenser is fitted in the turbine’s steam exhaust, while the power generators are connected to the factory’s heat recovery circuit to take full advantage of the thermal energy in the high-temperature cooling system of the Rolls-Royce gas engines.

This circuit is fed into the emergency air-cooler once heat recovery is completed, guaranteeing a return temperature of 79 à‚°C at the engine inlet at all times. Miguel Angel Martin explains that several factors influenced the selection of Rolls-Royce power for its upgrade: the positive experience it had gained with the original units, the guarantee of reliability levels, advice from an independent consultant and the aftermarket service provided by Rolls-Royce. The power systems specialist ensures engineering support and advice is always available to maximize performance of the cogeneration plant, thereby maximizing profitability. Rolls-Royce engineers pay routine follow-up visits to the plant.

Upgrade makes business sense

Jon Olano, technical manager at Inquitex, oversaw the transition between the earlier power units and the new B35:40V gas engines. He reports that in the first full month of operation the units achieved availabilities of 94 per cent and 96 per cent. “Today, high engine efficiency and reliability are fundamental to the profitable operation of a modern plant such as ours,” he says.

Inquitex’power plant building and offices, rationalist architechture in an industrial environment
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Gas consumption of the Inquitex facility has increased now the new trigeneration plant is installed and is equivalent to 50 per cent of the major city of San Sebastian. So relatively small increases in plant efficiency can make a big difference to profitability for Inquitex as it enters a new phase in its development. “We have big challenges and ambitious goals ahead but we are focused firmly on reaching the highest energy efficiency and the best performance,” adds Miguel Angel Martin.

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