钢铁行业ORC余热利用

Energy efficient electric steelmakingOrganic Rankine Cycle-based waste heat recovery systems for electric steelmaking are currently few and far between, but a recently installed system in Riesa, Germany and another underway in Brescia, Italy, could bring greater energy efficiency and has opened the way for similar applications.

By Alessandro Foresti* and Daniele Archetti**

Based on these objectives, Feralpi THE world’s first Organic Rankine Cycle will allow savings of up to 5% of total (ORC)-based waste heat recovery system EAF electricity consumption when there decided to install an innovative heat with power production in electric is no significant direct use of the off gas recovery system coupled with a totally renewed EAF fume treatment plant, steelmaking was started up on 18 thermal energy recovered.When, on the contrary, as in the case of employing evaporative cooling in ESF December 2013 at Elbe-Stahlwerke Feralpi (ESF) in Riesa, Germany. The successful ESF within the steel plant or nearby, the plant in Riesa (Germany). This site was start-up and the subsequent commercial possibility exists to utilise a portion of the chosen because it offered the opportunity operation demonstrated that ORC systems recovered EAF off gas heat directly and to export heat as steam to an industrial are a reliable tool available to steelmakers efficiently as thermal energy, the remaining client, thanks to an agreement with the to improve the energy efficiency of their heat available for power conversion by the local utility.ORC – and the electricity saved – is less. The ORC-based plant installed at Elbe-electric arc furnaces (EAFs). Stahlwerke Feralpi Steel Shop in Riesa is a Over 5,000 hours of actual operation and more than 10 million kWh produced are ORC-based Waste Heat-to-Power Combined Heat and Power (CHP) system. The saturated steam (approximately 30 sufficient proof that ORCs can withstand system at ESF Riesa (Germany)and match the peculiar conditions of A brief history of the EAF waste heat t/h) produced by the EAF fume treatment electric steelmaking, following the normal recovery project in Riesa[1] and the reasons evaporative cooling system has two operating routine of EAFs with highly behind choosing ORC technology might different destinations. Typically 20 t/h are variable loads, exhaust gas flows and help explain why the ESF example is now converted to power in the ORC to produce temperatures and with alternating power-being followed by other European mini-2.6 MW, while the remaining 10 t/h are sent to the nearby Goodyear Dunlop tyre on and power-off periods during melting mill operators. factory (Fig 1).or tapping and charging respectively.Feralpi, an important European A very important feature of the plant The continuous operation of the new steelmaker, producing long products for waste heat-to-power ratio installation the construction industry from plants in is the highly flexible heat-to-power in Riesa confirmed that the ORC system, Italy and Germany, considered installing a conversion: the ORC operates continuously automatically adjusting to the EAF new waste heat recovery system in one of with a variable steam flow rate between 2 operating cycle, does not distract the its electric steel plants in order to improve and 22 t/h, automatically adapting to the operators from their normal duties and EAF energy efficiency, reduce emissions different operating conditions of the EAF has minimum maintenance requirements. and cut operating costs simultaneously, system.The ORC plant was started up with A properly designed ORC-based waste maintaining overall plant availability and the first parallel on 18 December 2013 heat recovery system coupled to an EAF not increasing personnel.

Power output

TemperatureSteam Turbine(Traditional Rankine Cycle)Organic Rankine Cycle (ORC)Temperature

Industrial

thermal user

ORC

Industrial

waste heat recoveryCooling water systemEntropyEntropyeeee

eThermodynamic featuresOperation and maintenance costseeeeeee

e High enthalpy drop Superheating needed Risk of blade erosion Water treatment required High pressures and temperatures Specialised personnel necessary Convenient for plants > 10MWe Low flexibility Lower performance at partial load Small enthalpy drop No need to superheat No risk of blade erosion Non-oxidising working fluid Minimum personnel Automatic/self regulating High flexibility and good performance at Heat carrier loopOtherfeaturespartial loade Well proven in industrial heat recovery

Fig 1. EAF Heat Recovery Scheme at Elbe-Stahlwerke Feralpi Riesa, GermanyFig 2. Heat-to-power conversion with Rankine Cycles

*Alessandro Foresti, Turboden Srl, ITALY - alessandro.foresti@turboden.it - +390303552213

**Daniele Archetti, Turboden Srl, ITALY - daniele.archetti@turboden.it - +39 0303552431

April 2015

EAF off gasHeat (steam) recovered

Consteel fed EAFWaste heat boilerBrescia district heatingElectric energy

Electricity

Heat

Heat recoverysystem

90 t EAFTurboden ORC unit10 MWth district heating2,1 MW ORC Standard units from 200 kW to 10 MW Customised solutions up to 15 MWThermal energyCO2 saved: 10,000 t/y

Fig 3. Turboden ORC sizes and applicationsFig 4. EAF heat recovery scheme at ORI Martin, Brescia, Italyreaching nominal capacity the following last 15 years and currently operating record of ORC in industrial heat recovery in other energy intensive industries, the throughout Europe and elsewhere. day.steel industry has been slow to accept The start-up activities were completed the ORC concept. The first application in during the first half of 2014 reaching Turboden ORC UnitsTurboden was founded in 1980 by Prof. steel was a small unit in operation since uninterrupted continuous operation according to the EAF’s normal operating Mario Gaia to develop the research work February 2013 at the NatSteel mini-mill in started at Politecnico di Milano. Thirty-Singapore recovering waste heat from a routine.The plant is now in full commercial five years of work fully dedicated to ORC rolling mill billet reheating furnace.service and has demonstrated that it well development allowed the company to The breakthrough application at ESF’s exceeds the contractually guaranteed become Europe’s leader in ORC with electric steelmaking furnace in Riesa has opened the way for similar waste heat about 300 systems supplied worldwide.power output[2].Turboden ORC distributed generation recovery systems with power generation Why ORC instead of Steam Turbine?systems between 200 kWh and 10 in other EAF steelmaking plants. Today, Heat-to-power conversion is commonly mWh are used in renewables (biomass, the ORC is the easiest and most efficient achieved with Rankine Cycle systems where geothermal and solar) and in heat way of converting the exhaust gases of a working fluid is compressed by a pump recovery applications either bottoming highly variable discontinuous heat loads in and evaporated to the gaseous phase by reciprocating engines and gas turbines or melting furnaces. the heat of the hot source in a boiler. The converting waste heat to power in energy compressed vapour expands, spinning a intensive industries (cement, glass, metals) EU supportThe dissemination of the results obtained turbine to generate power. The expanded (Fig 3).Many of these ORC systems are at ESF to promote further application of vapour is then condensed by the cooling effect of the heat sink and conveyed to Combined Heat and Power Systems where the ORC process in electric steelmaking the ORC heat sink (low temperature heat gained the support of the European the pump to begin a new cycle. Traditional Rankine Cycle systems use discharge) is, in fact, a thermal user (space Union’s Sustainable Industry Low Carbon scheme through the project WHAVES water and steam as working fluid and are heating system, dryer or other).(Waste Heat Valorisation for more the most common solution for power units Sustainable Energy Intensive Industries)[4].above 20 MW where efficiencies above ORC and industrial heat recovery30% can be obtained using super-heated ORC systems demonstrated in different ESF’s successful experience led to a energy-intensive industries – such as second similar EAF project awarded to steam at high pressure/temperature. Organic Rankine Cycles employ working cement, glass, metals – that they respond Turboden, which is now well under way fluids with a heavy molecular weight well to the requirements of effective with start-up scheduled for year-end 2015. (siloxanes, hydrocarbons and refrigerants) industrial heat recovery installations. The The new 1.9 MW Turboden ORC will equip that guarantee dry vapour expansion simple, automatic, modulating, fail-safe the new waste heat recovery installation in all operating conditions. ORCs are operation of ORC systems can match the of ORI Martin steel plant, featuring a 90 typically preferred for smaller scale heat-actual process regime in all conditions, tonne Consteel-fed EAF (Fig 4). to-power systems up to 10 MW, due to maintaining overall system reliability.Brescia, Italy-based ORI Martin is a Decoupling from the main process higher efficiencies at lower heat source leading European supplier of engineering temperatures[3] and maximum ease of interface is a desirable feature in most heat steel (SBQ) for the automotive industry operation with minimum running costs recovery applications. This is facilitated and for general mechanical applications.by introducing a heat carrier between (no dedicated personnel necessary).The main difference between traditional the residual heat sources of the process Combined heat and power (CHP) Rankine Cycle with Steam Turbine and (typically streams of dust laden exhaust The ORI Martin system is also a combined gases) and the ORC unit.heat and power project where the thermal ORC is shown in Fig 2.Different heat carriers such as thermal heat recovered as steam from cooling EAF These operating advantages convinced oil, saturated steam or pressurised water exhaust gases is either exported to the ESF to choose the ORC solution.The superiority of ORC in small-to-can be used. Efficiency and investment district heating network of A2A, the local utility serving the entire city of Brescia, or medium-sized distributed generation costs depend on this choice.Notwithstanding the carbon intensity converted to power in the ORC to reduce systems is confirmed by the large number of units supplied by Turboden over the of steelmaking and the proven track electricity consumption at the steel plant.April 2015