Mitsubishi’s Ultra Steam Turbine

By Keith Henderson at March 03, 2011 08:43
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Mitsubishi Heavy Industries (MHI) announce their first order for a LNG carrier specifying their new Ultra Steam Turbine (UST) propulsion system offering improvements in fuel consumption and reduced emissions.

The vessel is a LNG carrier for Nippon Yusen Kabushiki Kaisha (NYK), with approximate dimensions of 123,000gt, LOA 288 m, beam 49 m. Scheduled for delivery during 2014 the gas storage capacity of 145,000 m3 will be divided between four spherical Moss type tanks. The Moss type tank is a spherically shaped LNG tank supported and fixed to the vessel by a cylindrically shaped skirt structure.

MHI’s Ultra Steam Turbine Plant (UST), is a new turbine propulsion system which claims to achieve approximately 15 per cent higher fuel efficiency than conventional steam turbine plants and is based on technology and experience gained from their numerous power plant applications. It is a steam turbine propulsion system because it not only includes advances in turbine and boiler design but includes a gearbox connecting two turbines to one output shaft

The UST differs from conventional steam plant by using a reheat cycle whereby exhaust steam from the high pressure turbine (HP Turbine) is led through a reheater that reheats steam up to boiler superheater outlet steam temperature, then is fed to the intermediate pressure turbine (IP Turbine). The HP and IP turbine share a common shaft. A separate turbine shaft incorporates the low pressure turbine (LP Turbine) and the astern turbine. The two turbine shafts are meshed in a gearbox to provide a single output shaft.

An Automatic Boiler Control System electronically manages the sometimes complex controls in the safe efficient operation of the system removing the variable of human judgement.

The present availability of the MHI UST system using the reheat turbine covers the 26 to 37 MW range. A more powerful 44 MW unit is under development and is aimed at the larger LNG carrier market using a twin screw arrangement.

 

Comparison of Basic Specification of CST vs UST Turbines (25MW base)
  Conventional Steam Turbine (Non-Reheat) Ultra Steam Turbine         (MHI Reheat)
MHI Type  MS36-2  MR36-II
Main Steam  5.68MPa x 520 9.8MPaG x 555
Reheat Steam  -  2.0MPaG x 555
Exhaust Steam  722mmHgv. x 27 728mmHgv. x 24
Shaft Generator  N/A  Applied
Thrust  25MW x 78rpm  23.5MW x 76rpm
Electric Output  -  1.5MW
Total  25MW x 78rpm  25MW x 76rpm
No. of Extraction 3 3
Feed Water Heater  3-stage F.W. system  2-stage F.W. system

 

Arrangement drawing of the MHI Ultra Steam Turbine System
(Credit: Mitsubishi Heavy Industries)

 

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