New Waste Heat Recovery System– challenges and solutions

Heimdal New Power Generator Project

Prepared by: Hydro: Unn Orstein, Project manager

Knuth Jahr, Mechanical Disipline LeadReinertsen: Morten Kongelf, Mechanical Discipline Lead

Petroleumstilsynet Seminar – exhaust stacks and waste heat recovery2007-02-07

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Introduction

l New cantilevered module to be installed on Heimdal summer 2008- Reinertsen AS is engineering and fabrication contractor

l Gas turbine from GE: LM 1600 gas generator with PGT 16 power turbineand ABB generator

- Iso rating 14 MW, Design case 10 MW- Exhaust data:

- 40 kg/sec 492 oC (10 MW)

- 33.7 kg/sec 523 oC ( 7 MW) – normal operating)- Max temp: 597 oC (3-4 MW)

l 11 MW hot oil waste heat recovery package (including silencer) - Letter ofIntent to Kanfa-Tec mid January

- Procurement direct to Kanfa–Tec and not via GE as planned

l The system has been improved - ref Åsgard B fire in the exhaust stack2005, and other experiences

l The hot oil heat exchanger is located ”in the bypass” to avoid:- Hot oil leakage into the turbine- Fire water inside the stack

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WHRU - hot oil systems - challenges

l Leakage from tube bundle in traditional vertical exhaust stack- Accumulates in bellows – textile a special problem- Tube rupture can result in > 3 M3 drainage to the turbine collector- Fire - due to oxygen in the exhaust, air during rundown of turbine and the

chimney effect

l Detect the hydrocarbon in the exhaust before the fire starts

l Drainage of hot oil

l Fire fighting system

l Damage to turbine and turbine casing due to fire and water

l Leakage from flanges in the hot oil piping hitting warm surfaces

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Alternative configurations evaluated

l Traditional configurationwith WHRU above theturbine exhaust outlet

l WHRU in the bypass stream

Silencer not shown

Exhaust Exhaust

Silencer shown partlyDrawings & photo from Kanfa-Tec

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Main issues in case of hot oil leakage

l Sump to collect hot oil leakage- Separate tank not shown on figure, 3 m3

l Detect liquid in sump- Drain test valve- Level indication

l Bellows should avoid:- small hot oil leakage into the exhaust

stream to collect in the textile and ignite

In case of leakage:- Close the louver (shut off air flow)- Nitrogen to inert the volume?- Drain the bundle to recovery tank- Fire water monitor on the LQ roof

Ideas:- Detection of hydrocarbon in exhaust?- Separate the 2 exhaust stream to avoid bellows?

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Material selection

l Ducting: AISI 321- Max operating temperature is 597 0C at 25 oC ambient - WHRU Supplier recommend design temperature of 593 oC

- Ambient temperature is normally well below the 25 oC- Max operating temperature is a transient case and not a normal operating case- Due to cooling of the outside of the duct- Duct downstream the bundle is exposed to lower exhaust temperature

- AISI 321 is the standard material for GE Energy LM1600 Exhaust Collector.

l Heatexchanger tube bundle/fins: ASTM A 106 GrB

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Duct leakages

l Design changes to reduce vibrations- avoid fatigue

- Rounded corners- Minimum temperature gradients- Avoid lifting ears or other additional

structures- reduced swirls

- LM 1600 has trippel diffusers in the Exhaust Collector

l Improved bolt design- Thermobolt has been specified- Bolt does not loose pre-tension during

turbine start cycle - Lover loads on bolts- Controlled compression loads on gasket

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Reduce potential for hot oil leakage from WHRU heat exchanger

l Improved bundle support- Avoid U-clamps interfering with the tubes- Possible tube contacts with screw, bolts etc is avoided

l Inspection of support of tube bundle during assembly

l The deck structure to be designed to reduce WHRU casing deflection

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Leakage from hot oil piping

l The following has been specified:- The hot oil/supply and return lines shall be welded to the WHRU

l Flanges are minimized and located away from hot surfaces

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Valve comparison

Louver – selected

Prol Smoother regulation in almost

closed position- Improved temperature control

l Improved flow distributionl Lower torque and material stressesl Pneumatic control system

Conl Leakage rate is 0.04 %l Pressure loss is higher – not critcall More moving parts

Flap (new type used on Grane)

Prol Improved sealing to avoid

oveheating the oil/cracking- Leakage rate 0.02 %

l Grane experience is positive

Conl Hydraulic control is required due to

high torque requiredl More expensivel Higher weight

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2 separate exhaust outlets - idea

Prol Avoid potential small hot oil leakage

into the exhaust to collect in thetextile in the bellow

l Reduce maintenance- Remove 2 bellows- Simplify removal of silencer and bundle

l Reduce weight

Conl The reduced velocity in case of part

load will have effect on dispersion Note: Turbine has excess power and a restriction in the outlet to increaseflow is possible

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Early detection of hydrocarbon leakage - idea

l Install suction probe downstreamhot oil heatexchanger

l Dual oven gas chromatographs to detect the hot oil

- Large differance between exhaust and hot oil fractions

l Plan to be issued for inquiry Februar 2007

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