waste heat recovery
control the exhaust flow velocity and distribution, and to collect the boiler washing water. MAN Diesel & Turbo recommends the installation of an exhaust bypass and bypass exhaust valves. It is further recommended that shipyards use computational fluid dynamics (CFD) to calculate and ensure an even exhaust gas velocity distribution into the boiler using guide vanes; this is important in securing a high WHR system efficiency.
Back pressure calculations for the exhaust system are also necessary to ensure the correct functionality of the WHR system. The correct exhaust velocity up through the exhaust boiler optimises functionality and minimises the risk of soot collection on the internal surfaces of the boiler.
Appropriate engine data can be provided by MAN Diesel & Turbo for exhaust systems with higher back pressures in cases where WHR systems and scrubber systems are combined: a situation that will arise with new ships serving routes in sulphur emission control areas. Total WHR system packages offered by MAN Diesel & Turbo can include an exhaust gas boiler, steam and power turbine generator units, PTO/PTI arrangements and power management. As a designer and supplier of main engines, turbochargers, steam and power gas turbines, the group says
it is able to optimise and
guarantee the performance of complete systems for yards and owners. The high efficiency of MAN’s latest TCA axial turbochargers allows more exhaust gas to be diverted for exploitation in power turbine-based energy recovery systems. In such applications, the power gas turbine is installed in the exhaust system parallel to the turbocharger and arranged to drive a generator via a reduction gearbox. The turbine may receive up to 12 per cent of the exhaust gas flow from the main engine. MAN Diesel & Turbo claims more than 30 years’ experience in developing, manufacturing and servicing power turbines. Of some 50 reference plants, most are marine installations. A co-operation agreement with Swedish energy and environmental technology company Opcon enables MAN Diesel & Turbo to exploit the potential of blending Opcon’s Powerbox
PAYBACK TIME FOR A TCS-PTG INSTALLATION SERVING A VLCC’S MAN B&W 6S90ME-C LOW SPEED MAIN ENGINE AS A FUNCTION OF FUEL PRICE
7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
300 400 500 *service: 280 days/year;1.4 USD/EUR 600 700 800 900 1000 fuel price (USD/t)
Voith weighs in with WHR system for smaller tonnage
A compact, advanced waste heat recovery system developed
by Voith promises a
significant reduction in fuel consumption and emissions from marine engine installations. The German group’s new SteamTrac system is said to be particularly suitable for shortsea cargo ships, ferries, fishing vessels and inland waterway tonnage. Heat from the exhaust system is tapped to warm up an operating medium in the evaporator and create superheated steam. Expanded into a piston expander, the steam is
WHR technology with smaller low speed engines to cut fuel consumption and emissions. The partners have examined the scope for re-using waste energy from low temperature heat sources. An Opcon Powerbox can be integrated with smaller engines than existing WHR units associated with higher temperature waste heat sources and large engines. Fuel consumption, and hence emissions,
can
An MAN TCS-PTG installation for a power station based on a PTG22 unit
94 I Marine Propulsion I February/March 2012
reportedly be cut by 5-10 per cent. A debut project for generating electrical power from waste heat will benefit a Wallenius newbuilding in which an Opcon Powerbox is integrated with an eight-cylinder MAN B&W S60ME-C8 low speed engine. • Important in calculating fuel savings and payback time for a power turbine-based system is the main engine load profile, MAN Diesel & Turbo explains. This is defined individually by the shipowner or operator with the TCS-PTG set up accordingly.
In the case of a six-cylinder MAN B&W
used to generate mechanical energy which can be fed back to the engine’s crankshaft or to a gearbox power take-in. The operating medium is liquefied downstream of the expander in a condenser and stored in a tank. The complete process is supervised and monitored by a control module.
The new technology can benefit newbuildings or can be retrofitted, says Marcel Flipse, executive vice president of Voith Turbo Marine SteamTrac BV, a newly formed company based in Twello, the Netherlands.
S90ME-C8.2 low speed main engine developing 31.6MW and propelling a VLCC, the maximum TCS-PTG output is reached at 90 per cent engine load. The TCS-PTG partly or fully replaces the contribution of a diesel genset, which consequently saves auxiliary engine fuel savings of 190 g/kWh.
Diverting some exhaust gas to the TCS-PTG increases the main engine fuel consumption slightly by 2 g/kWh, a fuel penalty deducted from the fuel savings of the auxiliary engine in calculating the overall savings.
The total cost of a TCS-PTG system estimated by MAN Diesel & Turbo includes installation and commissioning by the enginebuilder and yard. The payback time is accordingly calculated as a ratio of the total investment costs and the total fuel savings, using the exchange rate of 1.4 US$/Euro. At fuel prices of $650/tonne, a payback time of less than three years is achieved for the VLCC installation, whose engine is served by high efficiency MAN TCA axial turbochargers. MP
www.mpropulsion.com
payback time (years)
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