NEW TECHNOLOGIES IN COGENERATION APPLICATIONS: SIEMENS SGT-300 EVOLUTION MEETS MARKET REQUIRMENTS

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1 NEW TECHNOLOGIES IN COGENERATION APPLICATIONS: SIEMENS SGT-300 EVOLUTION MEETS MARKET REQUIRMENTS David Marriott Product Strategy Manager, SGT-300, Siemens Industrial Turbomachinery Ltd, UK Oliver Gruenig Sales Manager, Siemens Industrial Turbomachinery Ltd, UK Introduction SGT-300 history when introduced, sales to date, application types The SGT-300, then known as the Tempest, was introduced in Since that time over 70 units have been shipped and these units have accrued well over a million running hours in various applications. However, since that introduction 15 years ago, market expectations and technical capabilities of the Siemens business have changed. By introducing new technologies to the established SGT-300, Siemens have delivered a product which meets both today s legislative requirements associated with emissions and the key business needs of reliability and high plant thermal efficiency. The objective of the paper This paper will explain the impact of newly developed technology in improving market fit in terms of emission control, reliability and overall plant efficiency. The impact of these three critical advances in technology on European cogeneration applications will be clearly demonstrated. Market Trends The justification for installing a gas turbine power plant of any type invariably relates to finance. Financial directors of companies look for return on their investment (ROI) and require positive net present value (NPV), positive internal rate of return (IRR) and/or as short a payback period as possible. These financial parameters are all required for a gas turbine investment to go ahead. Consequently, the challenge to all gas turbine manufacturers is to develop their products to ensure maximum value for the gas turbine investment. The following sections discuss parameters that all have an effect on the gas turbine installation s financial indicators and discuss how they have changed over recent years to improve financial justification. Availability For the financial indicators for a gas turbine (GT) installation to remain positive, the plant is required to operate for as long as possible each year. With the closing of the spark spread (see below) over recent times, this has meant that the focus on plant availability has increased even further. Unfortunately, for continued high availability, a plant requires regular maintenance, during which time power is not produced. Market forces and drives for reduced total cost of ownership are reducing the maintenance activities required by the equipment manufacturers. Component lives are being increased and focus is on ensuring the GT remains running during spurious fault conditions where hardware/gt integrity is not at risk. The availability of a GT is measured using the ISO standard method given in equation X below. Availability =1 FOH + POH PH where, FOH = Forced outage hours

2 POH = Planned outage hours PH = Period hours As can be seen, availability is made up of planned and unplanned downtime components. The planned components are those downtimes that are due to the maintenance tasks required to ensure reliable operation. The average time required for planned maintenance tasks for GT s in the 7 to 8 MW power range is approximately 1.5% over a complete maintenance cycle. The unplanned components are those downtimes that are due to unreliability. Availability acceptable to the market has been around 95%. However, this is increasing and future values around 97% and above can be expected. Spark spread The majority of gas turbine installations operate on natural gas fuel. This has doesn t match was in next line many advantages over alternatives; it was tense?? cheap, abundant in many areas of the world and easy to burn with a low emission signature. To justify investment in a gas turbine installation, to replace an existing boiler and electrical import agreement, requires the fuel price to be as low as possible and the electricity price to be as high as possible. The ratio between the gas and electricity prices is often termed the spark spread ratio. As spark spread ratio increases, plants become more and more viable and Turkey's spark spread values of 3.5 or more provide excellent 6 opportunities for savings from a GT / / / / / / /2006 Figure 1. Turkey s spark spread Turkey EU Czech Rep Estonia Latvia Lithuania Hungary Poland Slovenia Slovak Rep Bulgaria Romania installation. Figure 1 shows spark spread values for various European countries including Turkey. It can be seen that, prior to 2005, the spark spread in Turkey was high, thus providing a positive incentive for gas turbine investments. However, since 2005 the spark spread can be seen to drop towards the more typical values seen in the EU, and this has ensured focus on cost awareness in order to maintain acceptable pay-back periods and other financial indicators. Fuel trends Natural gas prices have recently increased significantly and, in many countries, the associated increase in electricity prices has not been as great. The spark spread has therefore been diminishing, making GT plant justification harder and harder. Alternative fuels are still a minority sector for gas turbines; however, future market requirements for green power will increase the efforts being made to provide the capability to burn alternative fuels. When considering alternative fuels, the gas turbine manufacturer must ensure that the operability, maintenance and emissions signature all remain viable. Consequently, alternative fuels will take a long time to reach acceptance in the GT market. Emissions Many types of exhaust emissions are regulated around the world. The United States is one area where exhaust emissions are required to be most strictly controlled. Here, emissions of nitrogen oxides (NOx), carbon monoxide (CO), particulate matter (PM10 s) and volatile organic compounds (VOC s) (or non-methane hydrocarbons) are the most commonly regulated emissions. In 1990, emissions of NOx in the USA were regulated to 42ppmV. Now, in 2006, those same

3 emissions are soon to be regulated down to 15 or 25ppmV across the whole of the USA, then, in some areas, NOx emissions are restricted to as low as 2ppm. In Turkey, emissions levels are far less stringently controlled. However, Siemens commitment to the environment leads us to continue to provide world-leading emissions control technology in Turkey whenever practical. In Turkey, the emissions levels required are approximately 150ppmV for a machine of around 8 MW. The challenge for gas turbine manufacturers has been to achieve these low levels of emissions without impacting the reliability or availability of their product. NOx is produced in the combustor in areas of high temperature, so NOx emission control requires reduction of peak combustor temperatures. Initial solutions used either water or steam injection but, while these reduced NOx emissions to the required levels, the extra expense associated with providing a clean supply of demineralised water was prohibitive and, in some cases, this method compromised the component life of some machines. Dry low emissions are now possible and supplied by several vendors. This technology is based on controlling the air and fuel mixing, via premixing, so that the temperatures within the combustor are uniform and, via using lean burn, relatively cool. However, inherent in the premixed, lean burn philosophy is the reduction in turndown available when compared to diffusion combustion systems. Turndown is defined by the point at which the emissions of carbon monoxide increase to unacceptable levels when reducing GT output power. Diffusion systems can turn down to near zero load in most cases, however, premixed, lean burn systems generally can only turn down to approximately 50% load. This has serious implications in GT applications where power consumption cannot be guaranteed and this scenario is particularly evident in new developments that are expected to grow over a number of years. Efficiency The average air temperature around the world is slowly increasing. Many believe this to be due to the increasing amounts of greenhouse gases in the atmosphere. Greenhouse gases prevent infra-red radiation leaving the atmosphere, causing the temperature to rise. One of the main greenhouse gases is carbon dioxide and one of the major sources of carbon dioxide is the combustion of fossil fuels for transport and power generation. Technologies are being developed that will reduce the amount of carbon dioxide we produce. However, independent of these technologies becoming commercially viable, it is paramount that we extract as much useful energy from the fuel we burn. Traditional coal fired power stations extract approximately only 40% of the energy yielded by the fuel; a modern combined heat and power (CHP) plant can extract up to 90% of the energy yielded by the fuel. Subsequently a CHP plant, of around 8MW electrical output, can reduce the amount of carbon dioxide emitted into the atmosphere by 18,000 tonnes per year. Carbon dioxide emissions are now restricted in many countries in a drive towards satisfying the Kyoto protocol. Turkey has not yet ratified the Kyoto protocol but, in her desire to enter the EU, carbon dioxide emissions will become an issue. The reductions are monitored by CO2 allowances and the allowances are traded on the open market. Currently CO2 allowances

4 are trading at a value of around Euro20/tonne making the savings in the 8MW CHP plant worth 36kEuro per annum. This gives a financial incentive towards building the plant. Gas turbine installations provide both heat and power to the host site. Optimising the use of the heat and power produced is not always ideal, as the heat produced by a GT operating at maximum efficiency is fixed. Site heat requirements are often variable and, provided that the heat requirement is greater than that produced by the GT, the excess requirement can be provided by supplementary firing of the waste heat recovery unit (WHRU). Electricity can, however, in most cases, be exported to the local grid to provide an income and so, if the site electrical demand is smaller than the GT output, the GT can still operate at maximum efficiency by exporting power to the grid. Recognising this fact has led GT manufacturers to strive towards maximum possible thermal efficiency. This produces the maximum amount of electricity per unit fuel burnt but has the effect of reducing the exhaust heat available. However, for the reasons mentioned above, this ensures that the GT will be the best fit for a larger proportion of the heat and power market. GT efficiencies increase with GT size as the relative effect of losses becomes smaller. Figure 3 shows this trend. Simple Cycle Power Generation Gas Turbines Aeroderivativ 39 Electrical Efficiency (%) Electrical Output - MW(e) Figure 3. GT Efficiency trend SGT300 Developments to meet market requirements Availability The world over, Siemens products are associated with the very highest levels of quality. Siemens is committed to sustaining and enhancing this reputation and to being the most responsive source of solutions to improve operating plant competitiveness and profitability. Siemens strategic initiatives are all assigned to the three corporate programs of Innovation, Customer Focus and Global Competitiveness necessary to fulfill this commitment. Process harmonisation across organisational boundaries allows best practices and synergies to be more easily identified. This commitment is backed by R&D investment made annually to achieving gas turbine product quality and enhancement goals. The SGT-300 has consistently achieved availabilities better than 95%. However, Siemens recognizes that this still represents a significant amount of unplanned downtime and has instigated various programs to reduce this. Six Sigma methodology has been used from defining the problem through to implementing and controlling the solutions. The first part of the analysis involved retrieving data from site through the Siemens Electronic Data Exchange Network (EDEN). This system captures all data within the control system and sends it back to base in Lincoln. The data can be used for predictive trending and post analysis to investigate the true cause of fault

5 conditions. The EDEN link can also be used for remote assistance. This analysis showed three main areas where improvements could be made, namely, start reliability, running reliability and time to return to service. All three areas have been addressed and significant improvements in availability are already being seen through the EDEN system. Siemens target is to reach at least 97% availability on ALL units. Reliability World class reliability levels are required to achieve the levels of availability mentioned above. Siemens has been driving programs to ensure that its products maintain the world class reliability required. Issues that arise are given highest priority within the company until they are resolved for both existing customers and new users. All such issues with the SGT-300 have been solved ensuring the design targets for maintainability are met. Emission value (ppmv) Market perception is that GT reliability has been severely affected by the introduction of DLE combustion systems. This is not the case for the SGT-300. The Siemens lean-burn DLE NOx CO SGT-300 NOx and CO emissions at site 0 01/07/ /10/ /01/ /04/ /07/ /10/2002 Date Liquid fuel data Figure 4. Site emissions data Figure 5. DLE combustor liner after 32k hours operation Gas fuel data combustion system has shown world-beating reliability. The same system is used on the SGT- 100, SGT-200 and SGT-400 and the generic nature of the system has allowed problems to be solved easily and efficiently, with the solution being read across to all products. The system is reliable and consistently gives low emissions values. There are no moving parts and no requirement to set up the system on site. All control, to ensure reliable, consistent emissions figures, is done through software in the control system. Figure 4 indicates the emissions from an SGT-300, on both gas and liquid fuels, over a period of greater than one year, the NOx and CO values remain constant and very low. During this running period no changes were required to the system and this capability has been demonstrated on numerous other sites around the world. Figure 5 shows a DLE combustor liner from an SGT-300 that has completed more than 26,000 hours of full load operation. The liner can be seen to be free from any distortion or defect. The other components of the DLE system from this engine were in a similar, excellent condition.

6 Fuels experience The SGT-300 has been developed to burn various other fuels. Experience has been gained with rich fuels including gaseous LPG and liquefied natural gas (LNG) and for weaker gas fuels wobbe index values as low as 32MJ/Nm3 can be reached. This is equivalent to a methane fuel with approximately 20% inert content. Emissions The SGT-300 was originally introduced with the conventional, diffusion-flamed combustion system. As with all combustion systems of this type, the NOx emissions were relatively high and the CO turndown capability was very good. NOx emissions were reduced using either water or steam injection and the SGT-300 has running experience on both. Steam can be injected into the primary zone for maximum NOx reduction or into the compressor exit air which, as well as providing good NOx reduction, also allows the engine to produce more power. The market acceptance of steam or water injection is limited, as mentioned above, and so the Siemens lean burn DLE system was developed. The Siemens lean burn DLE combustion system is generic across the SGT-100 to SGT-400 products. The SGT-300 exhibits world class low levels of NOx emissions with this system. NOx emissions are expected to be as low as 8ppmV on gas fuel and 25ppmV on liquid fuel and this can be seen in figure 4 above which shows data from a customer s site. The DLE system has more than 3 million operating hours experience over a wide fuel and ambient temperature range; the system has no impact on GT overall performance and no associated reduction in reliability. The SGT-300 exhibits competitive levels of turndown. Developments to reduce the air flow entering the combustion system have shown significant improvements in turndown availability. Efficiency The SGT-300 has a competitive overall, open cycle thermal efficiency of over 32%. The efficiency achieved at site can depend very much on the details of the GT installation. If a waste heat recovery unit is employed then overall efficiencies can approach 90%, giving the savings in carbon dioxide production indicated above. Carbon trading is in place within the European Union QuickStart benefits at a Glance Save money low cost, web based solution at a fixed monthly cost with inclusive upgrades Avoid penalties through visible management of emissions obligations Reduce administration costs data integration and automation, all in a secure environment Reduce costs associated with risk via total visibility from a single EUETS picture (EU) via the Emissions Trading Scheme (ETS). Siemens is able to provide a complete end-toend, top-to-bottom solution for the EU ETS and beyond. This is via its QuickStart product which is a monitoring and compliance solution combined with a modern, fast, carbon trading system. Everything is web-based and it s available from Siemens as a subscription service hence there are zero rollout costs and no costly implementation project. Conclusions In conclusion the Siemens SGT-300 gas turbine remains a highly competitive solution for your power and heat requirements.