Client: Coldharbour Marine Ltd (CHM)

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Location: Nottingham, United Kingdom

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Project Status: Completed

 

Cooling System Investigation, Selection & Design

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A multimillion pounds project designed to allow for the Factory Acceptance Testing of all Inert Gas Generators ranging from 500Nm3/hr (0.5MW) IGG to 6000Nm3/hr (6MW) IGG. Fedem Consulting was commissioned to carry out FEED, select and design an evaporative cooling system to provide cooling requirement for the Inert Gas Generator:

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Fedem Engineering had to consider how to dissipate the process heat generated by the Inert Gas Generator (IGG) in a Factory Test environment when the normal "in-service" route of seawater cooling was unavailable.

The problem was defined as requiring an environmentally acceptable, cost effective and reliable method to achieving a combustion chamber cooling water temperature difference of 10 deg C.

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A literature review of the two main types of cooling systems; closed circuit cooling system and open circuit cooling system was conducted. We then went on to select and install the later, an open circuit evaporative cooling system due to its ability to achieve lower temperature approach; low capital and operating cost as well as lower power consumption.

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Piping and Instrumental Diagram (P&ID), control philosophy, alarm and setpoint list and sequence chart for the FAT facility cooling system was developed; and aided in the commissioning process alongside technicians.

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The cooling system has been commissioned and currently provides cooling requirements for the full range of manufactured IGG's during Factory Acceptance Testing. In addition, it provided cooling requirements for IGG plant during CHM successful Lloyds Type Approval Test.

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Root Cause Analysis Investigation and Development of Soft-start Sequence of Operation

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During FAT Testing, whilst performing first ignition test, CHM IGG experienced an explosion which led to the mechanical failure of combustion chamber flexible hose pipework.

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To mitigate the risk of further avoidable explosion, Fedem Consulting investigated the root cause of the explosion and persuaded senior management to implement a soft-start/stop sequence of operation. This saw the plant starting at a low fuel flow rate and low combustion chamber pressure, with vent valve set at 80% open position to provide adequate deflagration venting during ignition. The mode of operation was in accordance with recommendations set out in BS EN 416-1 and NFPA 69. The soft start/stop procedure was adopted, and various successful experimental test runs were carried out without further incident.

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Optimisation of IGG Combustion Chamber Pressure Requirement

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CHM IGG was designed to maintain an operating combustion chamber pressure of 200mbar. On-board ship, this pressure is achieved and maintained via a modulating valve located on the IGG vent line and a 2m deep barometric leg at the drain line of the IGG ensures a liquid seal is maintained in the combustion chamber, thus ensuring that no gas leaves the IGG via the water drain line.

As CHM FAT facility does not allow for a conventional barometric leg due to height restrictions and limitation in the facility layout, I was tasked to come up with a solution that would provide a barometric leg functionality.

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Fedem Engineering researched several efficient and cost-effective options - using control valve or restriction orifice plate. The research revealed that using a restriction orifice would solve the problem. The desired orifice nozzle size was then determined and specification sheet prepared. Overall control philosophy and sequence of operation for the new solution was also prepared.

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The use of restriction orifice plate has now been adopted by CHM as an alternative design option for retrofit vessels, as it provided barometric leg functionality during our successful Lloyds Register type approval test and subsequent factory acceptance test exercises.

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Inert Gas Dispersion Modeling using Flaresim

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​To address the concern of local authority and to demonstrate that the emission of combustion product
(inert gas) from CHM plant was within the EU recommended Environmental Assessment Level (EAL), Fedem Engineering was commissioned to undertake an Air Quality Impact Assessment using dispersion modeling.

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The assessment was used in support of planning application from the local authority. In the project, sets of combustion calculations were produced for the dispersion modelling. The calculations show how different anticipated combustion scenarios (complete and incomplete combustion) affects the formation of soot and NOx (air pollutants) during combustion process.

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Hydraulic Design of a cooling water systems using Pipenet

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The cooling water system has three heat exchangers in parallel, with a single pump driving the system. Fedem consulting was commissioned to model a closed-loop system using Pipenet software. The objective was to perform pipe-sizing calculation, select an appropriate pump and balance the system using orifice plates in order to eliminate excess flow.