developments True_Tree: A COST EFFECTIVE COGENERATION IN Working for over sixty years in the glass industry, Stara Glass concentrates on

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1 True_Tree: A COST EFFECTIVE COGENERATION IN by A. Santero, D. Cucci, E. Cattaneo, F. Prosperi, M. Placidi STARA GLASS S.P.A. INTRODUCTION All glass manufacturers know that it is impossible to transfer all waste gas heat to combustion air. In fact, it is wellknown that waste gas has a higher mass and higher specific heat than air; even in a modern and performing regenerative furnace, at least per cent of heat generated by fuel actually leaves the furnace with the C waste gas. Stara Glass is, today, deeply committed in studying techniques to exploit this otherwise lost heat. The Centauro system enables to save it as a hot clean air flow, but a further energetic advantage is offered by cogeneration. Stara Glass approached the problem of cogeneration by using an innovative external combustion engine, designed by Mr. Placidi, a highly experienced mechanical engineer, working in the glass and energy industries. The resulting and innovative True_Tree system lowers the waste gas temperature down to 200 C, recovering thermal energy and transforming a quota of per cent into mechanical and then electric energy. The remaining energy is recovered as 100 C clean air. Electrical energy thus generated Working for over sixty years in the glass industry, Stara Glass concentrates on can be directly connected to the local network and it stands as an immediate economic saving, which must be added to eventual relative environmental incentives. Hot air, depending on specific cases, can be used to warm up work areas, transformed into warm water for sanitary uses, or be considered as the first stage of a furnace heat recovery system, thus increasing furnace efficiency by per cent. Recovering waste heat in this way enables to save about per cent of melting costs. The True_Tree engine has been invented for solar and biomass research and development. The company s most recent studies regard methods to recover waste heat as always a big problem for glassmakers. The results of these studies can be seen in this article, where Stara has created a system to use this heat, by means of an innovative external combustion engine. applications, and has been adapted by glass technicians in order to provide an extremely simple, reliable and cost effective device, with a payback time of less than two years, without any impact on production lines. At present, True_Tree is the only cogeneration system specifically designed for glass furnace applications. PROJECT GUIDELINES Features and industrial strengths of the project: - the engine creates an open cycle with ambient air; - valveless two-stroke engine; 54 glass machinery plants & accessories 5/2012

2 SOLUTION FOR THE GLASS INDUSTRY - crank connecting rod balanced multi-cylinder engine; - crankshaft and crank connecting rod system are oil lubricated; - waste gas heat exchanger with micro-vibration. Moreover, compared to a Stirling engine, this open cycle eliminates size and cost of the cold heat exchanger. Furthermore, Stirling dynamic motions are hard to balance, while in this engine all pistons work on the same shaft, resulting in being easy to balance according to most common techniques. Compared to a Rankine cycle, an air engine eliminates the cost and size of the condenser. An air engine, such as a compressor, does not need specialized personnel for control and operation. Oil lubrication is a reliable and cost effective technology that prolongs the life of the device. The simplicity of the machine enables to limit maintenance, while the vibrating exchanger prevents the formation of dust layers on the waste gas side. The project can be engineered with common commercial parts. Air leaves the system at about 100 C. The engine is placed downstream from the furnace, avoiding interference with furnace operations. THE SYSTEM The heart of the system is represented by an innovative exchanger that allows to couple a huge exchanging surface to an open cycle exothermic engine, which is modular, valveless, and works at a low rotation regime, about 500 rpm. The cycle is not a Stirling, even if it is quite similar. In the present system, circuits are not pressurized, and there is no special gas or transfer to another cylinder, because the second cylinder is substituted by a feature of the thermal exchanger. The low temperature and pressure levels make the system identifiable as reliable and safe. glass machinery plants & accessories 5/

3 Operating cycle: - piston ascent: compression of cylinder air; - top dead centre: when pressure reaches a chosen value, the mobile exchanger enables air to come into contact with exchanging surfaces; - piston descent: the quick warmup causes an expansion of the air, which pushes the piston down; - bottom dead centre: when lights are open, the cleaning air expels hot air and fills the cylinders with cold air. True_Tree represents the most compact, cost effective and efficient system for thermal cogeneration. The thermal exchanger is made of easily interchangeable modules, which are protected from coarse dust by proper means. The submicron fine particles cross the exchanger, with exchanging surfaces constantly vibrating at ~7 Hz, thus preventing the dust from depositing. Surface temperature and fluid velocity also prevent the dust from depositing. If needed, a mechanical cleaning system can be installed. The device is completely thermally insulated and waste gas never comes into contact with cold elements (less than 200 C). ELECTRIC ENERGY PRODUCTION The True_Tree shaft is connected to a three-phase electric motor that can perform start-up and work as a power generator. Once the engine is started-up, the generated power, directly or by means of an inverter, supplies the net with the proper characteristics. If the user decides to utilize this power for the furnace (i.e. as a power booster), a group of condensers can supply the necessary reactive current. To start-up the device, it is necessary to let waste gas cross the heat exchanger until it reaches the correct temperature value. After this, the electric engine starts the True_Tree that, automatically, stops absorbing power and starts cogeneration. The device includes an automatic system of rotation speed control and an emergency system to stop operation in case of emergency. SYSTEM FLEXIBILITY Depending on construction type, the engine is designed in modules with one or two cylinders that can be installed in series by means of phasing keys, and therefore fits any plant size. Waste gas flow, rotation regime and waste gas temperature can be regulated. This means that True_Tree represents an alternative to all waste gas temperature reduction systems that are commonly placed before dust abatement plants. True-Tree therefore provides an important opportunity to achieve an economic advantage. This technology can be coupled with Stara Glass Centauro and, as shown in the next pages, it is also adaptable to plants that already include convective heat exchangers. Each installation will be customized basing on customers real needs, and considering furnace type, plant needs, available space, etc. APPLICABILITY IN THE GLASS INDUSTRY The glass industry is always interested in thermal recovery. The availability of an amount of hot waste gas ( C for regenerative and C for recuperative furnaces) can guarantee high electric generation efficiencies. The energy required to melt 1 ton of container glass is evaluated as MWh [ref: BAT Glass]. 56 glass machinery plants & accessories 5/2012

4 Therefore the estimated energy amount that is recoverable from the production of 1 ton of glass results about kwh. Modules Foreseen modules are compact elements including: - waste gas inlet; - waste gas outlet; - hot air outlet; - connection to electric network; - Instrument air supply connection. All requirements for installation consist in a waste gas line bypass and a relative extraction fan. If a fil- End Port or Side Port with bag filter or Mini-Centauro This analysis regards an End Port furnace where waste gas temperature must be lowered down to 200 C, the integrated solution allows to save all the relative heat, lowering waste gas temperature without any dilution. Twenty per cent of waste gas heat is transformed into electric energy, 62 per cent into hot clean air. Part of the clean air is sent to furnace regenerators with two advantages: combustion air temperature increases by about 50 C and regenerator efficiency increases by 1.89 per cent. The remaining hot air produced can be used directly for the warming of workplaces during winter and/or to provide services with water by an air/water heat exchanger. This solution enables to save 5.5 per cent of furnace fuel and to produce 75.4 per cent of electric power for boosting.

5 End Port or Mini-Centauro furnace with electrostatic filter This solution enables to recover waste gas heat by lowering its temperature down to 400 C, the common value for the usage of an electrostatic filter. With this method, 26.3 per cent of heat is turned into electric energy and 60.8 per cent into hot clean air. Part of the clean air is sent to furnace regenerators with two advantages: combustion air temperature increases by about 50 C and regenerator efficiency increases by 1.89 per cent. Computing prudentially foresees a 0.95 per cent of furnace energy saving. The remaining hot air produced can be used directly for the warming of workplaces during winter and/or to provide services with water by an air/water heat exchanger. This solution enables to save 1.4 per cent of furnace fuel and to produce 42.5 per cent of electric power for boosting.

6 End Port or Mini-Centauro furnace with convective heat exchanger This simulation considers a plant already provided with a convective heat exchanger to lower waste gas temperature without any dilution. The True_Tree engine is regulated in order to provide the convective heat exchanger with the necessary amount of heat to warm furnace combustion air up to 180 C, with two benefits: it increases outlet waste gas temperature by 100 C and improves regenerator efficiency by 4.10 per cent. Computing prudentially foresees a 2.05 per cent of furnace energy saving. The remaining hot air produced can be used directly for the warming of workplaces during winter and/or to provide services with water by an air/water heat exchanger. This solution enables to save 6.4 per cent of furnace fuel and to produce 49.8 per cent of electric power for boosting. Unit Melter furnace with bag filter This analysis regards an integrated solution where waste gas temperature is lowered down to 200 C. The integrated solution enables to save all the relative heat, lowering waste gas temperature without any dilution. The True_Tree engine expels waste gas at 200 C and air at 100 C, producing about 450 kw of electric energy. The hot air produced can be used directly for the warming of workplaces during winter and/or to provide services with water by an air/water heat exchanger. This solution enables to save 5.8 per cent of furnace fuel and to produce 53.3 per cent of electric power for boosting.

7 tering system is present, its fan is sufficient to let the system work, thus eliminating the need of a waste gas temperature abatement system. Examples of possible installation All simulation has been carried out considering the need of room warming for five months a year and a usage of 10 per cent of available hot water. Computing of economic benefits in Italy has been made with the advice of Consulet Servizi S.r.l., Savona. BENEFITS The economic benefits of the system are different in different countries, depending on energy costs and on economic incentives for energy saving and electric energy self-production. For example, for every 1,000 Sm3/h of 550 C waste gas, 22.5 kwh are produced (=197,100 kw year = toe), expelling waste gas at 300 C, while the amount of heat that is recoverable as hot air results about 26 toe. The chart on the next page shows the value of kw produced with 1000 Sm3/h of waste gas, entering True_Tree at a temperature (the parameter in the chart) between 450 and 700 C, and being expelled at C. Decreasing waste gas average temperature in the heat exchanger, the efficiency of the system is decreasing too, as can be seen in the chart. In any case, at a low waste gas temperature, high production of energy can be reached by using several modules. Obviously, the higher the efficiency, the more advantageous the investment. Each installation must therefore be studied for the relative plant, in order to achieve the highest benefits, with the lowest investment. Savings deriving from electric energy production are direct, and equal to produced energy costs. Saving deriving from white certificates must be added. Hot air can be used in many ways, Unit Melter furnace with electrostatic filter This integrated solution enables to recover waste gas heat by lowering its temperature to 400 C, common value for the usage of an electrostatic filter without dilution. The True_Tree engine works at its best efficiency, expelling waste gas at 400 C, air at 100 C, and producing about 300 kw of electric energy. The hot air produced can be used directly for the warming of workplaces during winter and/or to provide services with water by an air/water heat exchanger. This solution enables to save 4.5 per cent of furnace fuel and to produce 37 per cent of electric power for boosting.

8 Centauro Furnace True_Tree can be coupled with Centauro, increasing the benefits of this already highly performing system. This solution allows Centauro to save a further 2.2 per cent of furnace fuel, producing 18.1 per cent of boosting power. such as heating of the glass mix, drying of the sand, hot water production, but the simplest and most economical solution consists in room heating and the production of warm water. As an example, in Italy, 1,000 Sm3/h of waste gas can pay back between EUR 32,000 and 105,000 in the first five years, and between EUR 20,000 and 65,000 in the next years. The difference of results depends on the needs of the different applications. The data Stara Glass technicians need to simulate a possible custom solution are: - waste gas flow and temperature, considering to minimize infiltrations; - waste gas filtering temperature; glass machinery plants & accessories 5/

9 - cost of used fuel and lower calorific value; - cost of electric energy; - value of white certificates or other energy saving incentives; - fuel consumption; - utilized boosting power. Furthermore, since the system works only with waste gas, it can guarantee furnace operations during a blackout, substituting a continuity group. OTHER POSSIBLE APPLICATIONS True_Tree can easily be adapted to any system with heat sources that are warmer than 400 C, as in the fields of solar energy, biomasses, and cement and steel production. PROTOTYPE The first 1 kw True_Tree prototype is undergoing experimentation and testing right now, and once its efficiency has been proved, Stara Glass foresees the construction of a kw industrial prototype, 62 glass machinery plants & accessories 5/2012 and then to start production of the real scale engine during RESEARCH AND DEVELOPMENT Stara Glass has been believing and investing in research and development in the glass industry for more than ten years. The number of Stara Glass filed patents in spite of the present market crisis testifies the remarkable commitment of people and means for engineering sustainable solutions, in order to reduce glass furnaces consumption and pollutions. In addition to True_Tree, Stara Glass is also committed in other research projects: - advanced CFD studies on glass furnaces; - advanced techniques for NOx abatement; - cullet and glass mix preheating. With True_Tree we are convinced that we have found a very interesting product both from a technical and an economic point of view. All data of this article come from different experiences with scale models and mathematical simulations. Those who are interested in discovering the evolution of the first cogeneration engine especially designed for the glass industry, are invited to come and meet Stara Glass in Düsseldorf during the glasstec exhibition (22-26 October 2012, Hall 13, Stand A47), where the company s technicians will be present to demonstrate the latest of the project, to evaluate possible solutions and formulate estimates and forecasts of economic return on investment. STARA GLASS - HYDRA GROUP P.zza Rossetti 3 A/ Genova (GE) - Italy Tel: stara.green@hydragroup.it