Icetech paper the future of marine propulsion - gas hybrid power plants


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Icetech paper the future of marine propulsion - gas hybrid power plants

  1. 1. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 1 The Future of Marine Propulsion: Gas Hybrid Power Plants Edward James Eastlack Marine Engineer New Orleans, LA, USA ABSTRACT Rising fuel costs and increasingly stringent emission standards for the marine industry have caused ship owners to look at a wide range of marine technologies to meet environmental compliance and to reduce lifecycle costs. Emissions can be reduced in many ways including improved fuel quality, improved plant efficiency and after treatment. With distillate fuels, residual fuels and after treatment having high cost and equipment lifecycle costs, LNG appears to be the clear choice for helping the marine industry to meet these new emissions standards. The carbon footprint of a vessel can also be reduced by improved efficiency. Optimized natural gas prime movers and electrical systems can assist in achieving these efficiency targets. The International Maritime Organization (IMO) has also adopted greenhouse gas reduction measures by requiring an International Energy Efficiency Certificate (IEEC) and Ships Energy Efficiency Management Plan (SEEMP) for existing vessels and an Energy Efficiency Design Index (EEDI) for new build vessels after January 2013. Therefore, the industry must now address both emissions and plant efficiency. As a result, there is also increasing interest in fuel efficient “hybrid” propulsion/electrical systems. The latest systems use a common prime mover that does not have to have a fixed frequency to accommodate the electrical system. Several new system designs are adopting this concept where generators are able to operate at variable speed, and all outputs go into a common DC grid or bus system. From there, the DC is converted to whatever voltage and frequency a particular load or system needs, using VFD technology to achieve improved plant efficiency or fuel economy. Hybridization of the power plant can improve the transient response of gas engines as well as provide additional load profile flexibility and reduced running hours on the prime movers which translates to improved efficiency and reduced carbon emissions. These alternative sources of energy are easy plug and play options to the existing DC grid or bus system. There are many options for hybridization to include high powered lithium battery banks, wind turbines, solar panels, fuel cells, super capacitors and micro turbines. The Organic Rankine Cycle using refrigerant or critical CO2 gas has also gained acceptance as an effective means to recover waste heat from low heat sources such as engine jacket water and exhaust gases, thus, improving plant efficiency even further. Optimized bow, hull, propeller and rudder design are additional ways to improve efficiency and reduce carbon emissions. Gas hybrid power plants with waste heat recovery systems and optimized hydrodynamics offer ship owners the right combination of marine technologies needed to reduce fuel consumption, emissions, lifecycle costs as well as improved reliability and durability of shipboard propulsion systems. INTRODUCTION In order to reduce the carbon footprint of the global marine industry, the International Maritime Organization (IMO) has adopted a greenhouse gas reduction regime from a marine power plant efficiency standpoint. Improving power plant efficiency essentially involves burning less fuel and, thus, emitting less carbon to the atmosphere. IMO power plant efficiency requirements for existing vessels include a Ship Energy Efficiency Management Plan (SEEMP) and International Energy Efficiency Certificate (IEEC) and are required after January 1, 2013. The SEEMP and IEEC are retroactive to existing vessels and will be required to retrofit marine technology that results in a 10% plant efficiency improvement at the next regularly scheduled dry dock after 2013. New build vessels will additionally be required to have an Energy
  2. 2. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 2 Efficiency Design Index (EEDI). Gas hybrid propulsion is the perfect combination of marine technologies because it provides reduced emissions and improves power plant efficiency. The emissions benefits come from burning clean and abundant fuel (natural gas) and the increased efficiency of a hybrid electrical propulsion system. MEDIUM SPEED (OTTO CYCLE) LEAN BURN NATURAL GAS SPARK IGNITION ENGINE The Bergen B35:40 is a good example of a lean burn Otto cycle spark ignition marine gas engine currently available. The emissions of this engine meet all current and future requirements to include Tier 4 without after treatment. The Bergen lean burn spark ignition gas engine operates according to the Otto Cycle using a lean mixture of gas and air as it is compressed and ignited by an electric system. A lean burn engine operates at air excess ratios of 1.8 and higher, and as the illustration shows, this gives increased power, efficiency and reduced NOx emissions. This is achieved by improving the combustion system so that the ignition energy is capable of firing such lean mixtures reliably. Additionally, a highly efficient turbo charging system is used to take advantage of the possible power increase offered by the extended knock limit of lean mixtures. Air is drawn in by the turbocharger through the charge air cooler and into the cylinder. A timed mechanical gas valve injects gas into the inlet air stream to ensure a homogenous and lean mixture of air and gas. Air flow is controlled by the variable turbine geometry of the turbocharger while gas flow is controlled by mechanical valves before each cylinder. The gas pressure is set electronically by the pressure regulating valve on the fuel gas supply module ahead of the engine. An air flap for each cylinder restricts the air supply during start-up and low load operation. As the pressure in the cylinder is low, gas is admitted into the small pre-chamber in each cylinder head, electronically controlled by the pre-chamber pressure unit. During compression, the lean charge in the cylinder is partially pushed into the pre-chamber, where it mixes with the pure gas to form a rich mixture that is easily ignited by the spark plug. This powerful ignition energy from the pre- chamber ensures fast and complete combustion of the main charge in the cylinder. Advanced electronic engine management ensures the operating parameters of the engine are adjusted and optimized in relation to each other. The system sets the optimum main and pre-chamber gas pressures, air/fuel ratio, fuel rack position, ignition timing and throttle position. The alarm and monitoring part of the system features many built-in safety functions. It combines safe operation with high availability, protecting the engine and signaling any fault. It includes a misfiring detection system based on analyzing different operational parameters and a knock detection system. The system detects and eliminates knocking individually for each cylinder. The complete engine management, control and monitoring system fits into a cabinet next to the engine and communicates with the plant control through one simple cable (RR). Figure #1. Hybrid Propulsion. Retrieved from “Bergen B35:40 gas engine,” by Rolls Royce Power Engineering June, 2009. NEW GENERATION ELECTRIC PROPULSION SYSTEMS (DC GRID) The Siemens Blue Drive Plus concept implements a new control philosophy into the traditional diesel electric propulsion systems such as variable speed operated diesel engines and load shifting. This technology makes possible low emissions of greenhouse gases, low fuel consumption, and full utilization of gas/dual fuel systems and SCR systems to reduce NOx emissions. Additional benefits are extended maintenance intervals of the prime movers, reduced space requirement for the electrical system, increased efficiency of the electrical system, clean power supply to the auxiliary consumers and no rectifier transformers. Prime mover speed control is possible through the whole speed range of the engine. The control system
  3. 3. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 3 will dynamically set the speed according to the optimal operating point of the engine which is essentially the lowest possible specific fuel consumption (g/kWh). During DP operation, the advantages are substantial as production and even spinning reserve can be realized with limited consumption, emissions and maintenance cost. In low load situations the power management system will load shift to one engine or alternative power supply if the system is hybridized. There is a need for some predication software based on history or pre- determined trip performance for low load conditions. Also, the ramp up time of the engines for large step loads is longer as the mass needs to be accelerated and the turbochargers need to become active from the lower flow rates over the turbines. Therefore, with some of these engines, optimization of the engines is needed, or multi stage turbo charging, or turbo bypass at low loads. The system also has the capability to shift load from port to starboard as required. Electrical power generation is typically accomplished using synchronous generators designed to operate at the same speed or power range of the connected prime mover. The Blue Drive Plus system makes it possible to consolidate the generator, bus-tie panel, and frequency converters for all auxiliary drives. If DC distribution is used a separate inverter may be required depending on the application. For general service loads the AC inverter might be consolidated to a particular load center but large electric motors would have their own to reduce power consumption. Harmonic distortion associated with rectifiers and frequency converters is effectively isolated by the DC bus unless there are loads coming directly off the main generator before the inverter which is not typical. This consolidation allows for clean power to be supplied to all auxiliary consumers and reduces the total package footprint by 30%. Figure #2. New Diesel Electric Propulsion System. Retrieved from Blue Drive Plus C,” by Siemens Corporation July, 2010 The new control philosophy monitors all generator control, drives control and power management functionality in one unit. The speed and power of the prime movers are controlled in correspondence with the total power consumption of the vessel. The electric system is only fed with active power from the generators, thus, eliminating the need to handle reactive power. The speed and power characteristics of the prime mover will be parameterized. There are three main integrated components that make the Blue Drive Plus system which include the power management system, the power plant protection and generator power adaption systems. There are two parts to the Power Management System. The first is total load versus available power. There is also a follow up that occurs with the DC system and that is optimizing engine load against fuel consumption and engine speed. The latter is controlled by a data base of the engine fuel consumption performance at different speeds and load capability. Once the load per engine is known, the system will match the best fuel consumption figure and set the engine speed accordingly. The system uses an algorithm that will perform fast differential equations to find the minimum fuel consumption. The fuel flow metering system for the engine provides the needed feedback to the system. The control system uses fast computers able to perform the necessary calculations and also a power system that is not speed dependent. AC systems are speed dependent which require isochronous governors which essentially put a lot of unnecessary wear and tear on the engine due to constant adjustment of the fuel rack to maintain constant speed. The DC system power basically comes from alternators connected to solid state rectifiers which
  4. 4. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 4 effectively stop reverse power issues, but the rectifiers can be active front end types that can adjust the alternator performance to unity power factor as well, reducing conductor sizes and installation costs. Active front ends on drives and rectifiers means they are adjusting the firing angles of the rectifiers to achieve a unity power factor or in some cases negative. In this way a conventional vessel with a lot of the AC to DC drives can use these devices to correct system power factor as well as provide rectification. Figure #3. Fuel Consumption Comparison. Retrieved from Blue Drive Plus C,” by Siemens Corporation July, 2010 This might be typical on some newer offshore vessels or ferries. This essentially means a smaller generator and cables due to reduced AC current. If there are no AC loads directly on the generator from the vessel this is not an issue because the power factor can be adjusted with an automatic voltage regulator depending on the vessel requirements. The engine, although turning slower can have reduced speed effect on voltage compensated for by excitation control. The DC grid also makes it easier to connect to shore power regardless of voltage and frequency differences. A back up battery bank can charge while connected to shore power and be a temporary source of power while in port. The DC Drive concept makes new energy sources a plug and play option, so your drive system essentially never becomes obsolete. HYBRIDIZATION OPTION 1&2 - WIND TURBINES AND SOLAR PANELS An effective power plant hybridization option is wind turbines and solar panels. This is an easy plug and play option to the DC Power Grid concept. Solar panels are virtually maintenance and are ideal for charging storage batteries. The photovoltaic Cells are encapsulated between a tempered glass cover and an EVA pottant with PVF back sheet. The entire laminate is installed in an anodized aluminum frame for structural strength and ease of installation. Solar panels are designed to convert sunlight into electricity. The current and power output of a solar panel or photovoltaic module is approximately proportional to sunlight intensity. At a given intensity, a module’s output current and operating voltage are determined by the characteristics of the load. If that load is a battery, the battery’s internal resistance will dictate the module’s operating voltage. Wind turbines and solar panels can be mounted in various configurations onboard a wide variety of vessels to harness wind and solar energy which is very abundant out at sea. The type of vessel will determine the best configuration for optimizing the available energy. A wind turbine is a rotor blade driven 3-phase alterna designed for low speed operation. The rotor component includes the blades for converting wind energy to low speed rotational energy. The generator includes the windings, gearbox and transmission which converts the low speed rotational energy to electrical energy. These machines are extremely efficient in low wind speeds yet capable of producing 500 watts or more depending on allowable space (TMP). This technology allows the vessel to harness renewable energy to reduce fuel consumption and greenhouse gas emissions. This technology can also assist a ship owner to meet the ever changing MARPOL regulations. HYBRIDIZATION OPTION 3 - HIGH POWER LITHIUM BATTERY BANKS Power plant hybridization is also possible using lithium polymer ion batteries. These batteries have been used for commercial and military marine applications. A typical battery bank will include a
  5. 5. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 5 battery management system with connecting cables and communication harnesses to the vessel systems. The battery modules can be combined to produce megawatts of power that can replace a prime mover. These battery banks can act as the sole energy source for low load situations, handle peak loads without starting standby generators and act as an energy buffer. This energy buffer will optimize fuel consumption, emissions, lifecycle cost and transient response to power demands. This is especially important for gas engines which have slower transient response than their diesel counterparts. HYBRIDIZATION OPTION 4 - FUEL CELLS FOR MARINE APPLICATION Another marine power generation option using natural gas for fuel is a marine application of a fuel cell. Wartsila is currently developing fuel cell technology for marine application in the power range of 5MW. The Wartsila FC50 is 50KW and the FC250 is 250KW. Scalable systems will be available up to 5MW. Figure #4. Wartsila Solid Oxide Fuel Cell. Retrieved from Wartsila Fuel Cell Program,” by Wartsila Corporation July, 2010 Commercial marine applications are targeted for auxiliary power units. This technology could also be integrated as part of a hybrid solution for propulsion systems in conjunction with combustion engines. The hybrid solutions between the ship’s main engine and fuel cells are systems available through Wartsila, Siemens, ABB, Converteam as well as others. Fuel Cell technology using natural gas as fuel offers ultra low emissions and high thermodynamic efficiency which makes for an excellent application for coastwise shipping, inland waterway and offshore applications and operations inside the North American Emission Control Areas. The high operating temperature of SOFC technology enables co-generation where the high value exhaust heat can be utilized in marine applications to produce electricity, steam and cooling—even freezing, depending on the vessel type. Recovery of the waste heat which is a byproduct of the chemical reaction can raise the efficiency to as high as 90%. Additional byproducts of the chemical reaction include water, electricity and small amounts of NO2 depending on the fuel source. Fuel Cell benefits include high efficiency (40-60%), ultra low emissions, low noise, no vibrations, co- generation, fuel flexibility, high part load efficiency, high reliability and availability (WC). Figure #5. Diagram of Fuel Cell Process. Retrieved from Wartsila Fuel Cell Program,” by Wartsila Corporation July, 2010 The fuel cell works by passing streams of fuel and air over electrodes (anode and cathode) separated by an electrolyte. This produces a chemical reaction that generates electricity without requiring the combustion of fuel or the addition of heat typically required in traditional primemovers and provides another method for producing electricity from fossil fuels (natural gas). HYBRIDIZATION OPTION 5 – SUPER CAPACITORS Another hybridization option is the use of super capacitors. Super capacitors can provide stability and efficiency to the DC grid. A super capacitor can provide a few seconds to a minute of reactive power in cost effective package. A 20 foot container can provide 1MW of power for 1 minute. Super capacitors have a longer life than lithium battery
  6. 6. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 6 banks and are ideal for shipboard application because of their superior high power charge/discharge cycling with lifetimes over a million charge/discharge cycles at 100% depth of charge (MT). EFFICIENCY IMPROVEMENT OPTION 1 - RANKINE CYCLE AND EXHAUST GAS WASTE HEAT RECOVERY (CO2) The Rankine Cycle when using super critical CO2 as the working fluid can eliminate the need for using thermal oil as the intermediate working fluid because super critical CO2 has very high thermal efficiencies at temperatures above 500C and 20 Mpa. For example, capturing exhaust gas waste heat using CO2 would allow for the CO2 to be circulated directly through the exhaust gas heat exchanger and power the turbo alternator directly, making electricity. A Caterpillar G3516 engine has 863F exhaust temperature and 20526 lb/hr exhaust flow rate at 100% load. The compromise is the higher working pressure for a super critical CO2 system is around 3000 psi. A system like this using CO2 as the working fluid would require high speed turbine alternator power electronics to deliver the required DC voltage would be needed to plug and play into a DC grid system. The turbine can be custom made to add approximately 10-20% efficiency to any primemover without taking up a lot of space. This can be megawatts of power depending on the size of the prime mover producing the waste heat. A high pressure pump is needed to establish super critical pressure. This pump located on the outlet side of the condenser is electrically driven. A recuperator is used to improve process efficiency and reduce the net losses of running an electrical pump. A condenser is used to liquify the CO2. The exhaust gas heat exchanger consists of a finned-tube coil attached to the prime mover exhaust piping after the turbocharger. It is designed to capture waste heat from the exhaust stream and apply it to the Rankine Cycle working fluid circulating through the coil. Figure #6. Diagram of Super Critical CO2 Rankine Cycle. Retrieved from Marine and Power Engineering Products,” by Marine and Power Engineering Inc February, 2012 . EFFICIENCY IMPROVEMENT OPTION 2 – OPTIMIZED HYDRODYNAMICS Improved bow design can reduce hull resistance and improve fuel efficiency. The new bow design developed by Rolls Royce gives better performance in a seaway, less speed reduction, reduced accelerations and less risk of hull plate deformation in the fore body in high seas. The design combines a vertical leading edge with a bulbous lower section and flares in the upper section. The design was developed using computer simulation an 8 percent reduction in resistance when compared to a conventional raked bow with bulb. Accelerations in the forward part of the vessel are reduced by 10 percent. The use of computational fluid dynamics assisted with optimizing the hull for reduced resisitance. The computer based work was verified in tank testing models. Rolls-Royce is applying the bow design to a wide range of vessel types such as passenger, ropax and roro ships, chemical and product tankers, LNG/LPG Tankers, bulk carriers, LNG bunkering vessels and superyachts. This bow design is also easier to construct as it has fewer double curvature plates and can be lighter due to the reduced impact from the waves (ID). EFFICIENCY IMPROVEMENT OPTION 3 – OPTIMIZED PROPELLER AND RUDDER DESIGN Improved propeller and rudder design is another efficiency improvement option. Rolls Royce has an integrated rudder and controllable pitch propeller system (Promas) which improves propulsion efficiency by 5 to 8 percent. There is a strong low
  7. 7. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 7 pressure vortex behind a traditional propeller that acts on the propeller hub increasing drag and reducing propeller thrust. A special hubcap is fitted to the propeller, which streamlines the flow onto a bulb that is welded to the existing rudder, effectively reducing flow separation immediately after the propeller. The result is an increase in propeller thrust as previously wasted energy is recovered from the flow. The addition of the bulb on the rudder also streamlines the flow aft of the rudder, further reducing drag. The hubcap is mounted outside the propeller hub and acts purely as a hydrodynamic fairing and no special hub design is needed, with cost and technical complexity kept to a minimum. Adopting the twisted rudder design of the Promas system can yield further improvements in efficiency and maneuverability (ID). This kind of system can be installed during a regularly scheduled dry docking and is a simple retro-fit to improve power plant efficiency and meet the impending IMO efficiency requirements for existing vessels as well as newbuilds. CONCLUSIONS AND RECOMMENDATIONS A ship owner that is aware of the regulatory requirements for marine power plant emissions and efficiency will be well positioned to keep existing vessels compliant as well as design newbuild vessels to meet the EEDI. Environmental compliance measures mandated by the IMO to reduce emissions from a power plant efficiency standpoint puts a new twist on the increasingly stringent emissions reduction regime. This leaves the owner with existing vessels that must be retrofitted with efficiency improving technologies. Fuel quality can also improve emissions and reduce carbon emission. Thus, giving renewed motivation to switch to LNG. Power plant efficiency can also be improved by an optimized electrical distribution system such as a DC bus or grid. In a DC grid system the generators operate at variable speed and all outputs go to a common DC grid. The DC is then converted to whatever voltage and frequency a particular load or system needs, using VFD technology to achieve improved plant efficiency or fuel economy. Additional improvement to plant efficiency is achieved with several power plant hybridization, waste heat recovery and hydrodynamic optimization options. The power management system senses the available energy sources on the grid such as optimized gas engines, capstone micro turbines, fuel cells, wind turbines, solar panels, or super capacitors. Depending on the existing load, the power management system will load shift to the best applicable energy source as required. This allows for load profile flexibility and thus operational flexibility of the power plant. The Organic Rankine Cycle, using an applicable working fluid such as an environmentally friendly refrigerant gas like R245fa or critical CO2, is another effective option to raise power plant efficiency by recovering heat from engine exhaust or jacket water and creating DC power that plugs right into the grid. Optimizing the bow, hull, propeller and rudder can also improve efficiency. Hybridized marine power plants using natural gas for fuel, waste heat recovery systems and optimized hydrodynamics offer ship owners the right combination of marine technologies needed to reduce fuel consumption, emissions, lifecycle costs as well as improved reliability, operational flexibility and durability of shipboard propulsion systems. REFERENCES CE. (2012, Jan). Hybrid marine propulsion. Corvus Energy. EMP. (2012, Jan). Wind and solar power for ships. Eco Marine Power. ID. (2011, Nov) Innovative Gas Powered Design. In Debth. http://www.rolls- /publication.pdf MEPC. (2011, July). Mandatory energy efficiency measures for international shipping adopted at IMO environment meeting. Marine Environment Protection Committee – 62nd Session. mepc-ghg.aspx MPE. (2012, Feb). Super critical CO2 Rankine Cycle Waste Heat Recovery System. Marine and Power Engineering, Inc. MT. (2012, Feb). Ultracapacitor grid storage solutions. Maxwell Technologies. storage RR. (2009, April) Bergen B35:40 gas engine. Rolls Royce. http://www.rolls- SC. “Blue Drive Plus C” Siemens Corporation, Jan, 2007.
  8. 8. Paper No. ICETECH12-XYZ-R0 Eastlack Page number: 8 nergy/marine/Pages/Newdieselelectricpropulsionsystem.aspx TMP. (2012). Wind Generators. Trans Marine Pro. WC. (2005, Jan). Wärtsilä fuel cell program. Wärtsilä Corporation. rtsil%C3%A4%20Fuel%20Cell%20Program.pdf AKNOWLEDGMENTS I would like to thank Professor William Sembler for his guidance and support during my courses of study. This course of study has led to my involvement with the Gulf Coast Advisory Council on the use of LNG as a Marine Fuel. The Gulf Coast Advisory Council is led by David Braxton Scherz of Det Norske Veritas (DNV). The California State Lands Commission has asked me to sit on their “Future Fuels” panel at the 2012 Onshore and Offshore Pollution Prevention Symposium in October 2012. rst/Prevention_First_Home_Page.html I will also be making a presentation covering key points from my research on LNG as a viable marine fuel. The work being done by the GMU Consortium Advisory Committee for promotion of U.S. Marine Highways should also be acknowledged. highway/document/GMU-Mar-Hwy-Res.pdf This work is vital to the country buying into a more efficient marine transportation system and, hopefully, choosing LNG as a cost effective and environmentally friendly fuel. The abundance of natural gas represents energy independence for the United States and essentially marine transportation independence. Coastwise Jones Act new build vessels will be prime candidates for gas hybrid propulsion plants due to their frequent operation in the Environmental Control Areas which will require a cleaner fuel and more efficient power plant to meet the ever increasing emissions and energy efficiency standards. The enormous response from people in the Industry who are responsible for the new build programs as a result of my thesis, Natural Gas as a Viable Marine Fuel in the US, must also be acknowledged. Environmental compliance of their vessel fleets is a key issue to be addressed. The economic and environmental benefits of gas hybrid propulsion systems will take any fleet owner to the next level. The benefits of natural gas as a fuel has been known for a long time, but has only recently been recognized globally due to a lack of understanding of the intricacies of working with LNG in this regard. It is my hope that this paper and my previous paper “Natural Gas: A Viable Marine Fuel in the US,”http://www.maritime- fuel-in-the-united-states will help remove previous roadblocks in this respect and help to initiate new build programs and conversion projects, incorporating proven marine technology that provides lower emissions and higher efficiencies. APENDIX A