Cowdenbeath Area Committee
2nd December, 2009
Agenda Item No. 6
MONITORING OF AIR QUALITY AT MOSSMORRAN & BRAEFOOT BAY
This summary is intended as a background document in support of the presentations that are planned for the Cowdenbeath Area Committee meeting that is scheduled for 2 December 2009.
The Mossmorran & Braefoot Bay Independent Air Quality Monitoring Review Group (Review Group) was set up over 20 years ago and has an ongoing remit to assess air quality in the areas around the facilities at Mossmorran and Braefoot Bay. The members of this Review Group include representatives from Fife Council, NHS Fife, Scottish Environment Protection Agency (SEPA), the
Institute of Occupational Medicine (IOM), and local Community Councillors. Representatives of the operating companies, Shell and ExxonMobil, are invited to attend the meetings of the Review Group.
Amongst the issues of primary concern is the air-quality impact of flaring.
ExxonMobil produces ethylene at its Fife Ethylene Plant from gaseous ethane supplied by the adjacent Shell Fife Natural Gas Liquids plant. Both plants operate continuous processes. The ethane feedstock received from Shell is a by-product of the natural gas refining operations at the St Fergus
Plant, Peterhead. Shell separates out and delivers the ethane to ExxonMobil, and produces its own products from the remaining constituents.
Flaring is an integral safety feature of the process at the ExxonMobil Plant as it is not possible to switch off the supply of ethane from the North Sea installations to the Shell Plant. For this reason there is an operational requirement to have a facility for flaring in the event of a plant shutdown. The flares are specifically designed to safely dispose of large quantities of hydrocarbons by burning them to produce carbon dioxide, water vapour and a very small quantity of unburned hydrocarbons. The height and design of the flare ensure that the unburned hydrocarbons are dispersed in the atmosphere at harmless concentrations. In addition, steam is supplied to the top of the flare to improve combustion and reduce the formation of dark smoke. The steam injection, however, can lead to unwelcome noise and vibration. Therefore, the optimisation of the ‘steam balance’ to ensure efficient combustion while minimising noise and vibration is the key to managing a flare event. Steam is fed continuously to the flare stack so that it is ready to receive hydrocarbons at any time.
At Mossmorran there are 2 ground flares and one elevated flare and the ground flares are used in preference to the elevated flare where possible. The main constituent of the gas that is flared by
ExxonMobil is ethane which burns very cleanly and very brightly. Periodically, when the entire plant is scheduled for maintenance (such as in the summer of 2008), gases are flared so that operations at the Plant can be shut down safely. However, flaring at such times is at lower rates than during unplanned shutdowns and this process generally does not lead to complaints. The next major shutdown is planned for summer 2010.
ExxonMobil operates the Fife Ethylene Plant under a strict set of conditions as stipulated within the
Pollution Prevention and Control (PPC) Permit issued by SEPA. This Permit recognises the operational necessity for flaring from time to time but the company is required to record the tonnage of gas flared so that the resulting total mass emissions of each flare event can be quantified. These figures are included in end-of-year performance reports submitted to SEPA. The company is also required to investigate and report on the cause of major flaring incidents and SEPA carries out its own investigations following these events. The outcome of the investigations is used to assess compliance with the Permit. Copies of these reports are held on SEPA’s Public Register in Perth and are accessible to members of the public.
Over the years, studies comprising community air monitoring, stack monitoring and air quality modelling have concluded that during normal operations and during planned flaring there are no significant effects on the local air quality and no adverse effect on local health. ExxonMobil carried out an extensive study of air quality in the community in the summer of 2008, before and after flaring activities/

- 2 - activities associated with a planned shutdown. This study was reviewed by the Review Group and found to be consistent with earlier studies that showed no significant impact. As a requirement of the
SEPA Permit, both ExxonMobil and Shell have recently submitted a modelling report which predicts worst case emissions from each plant separately and in combination and this will be reviewed by
SEPA and by the Review Group.
Flaring at ExxonMobil Mossmorran
The summary below gives an outline of unplanned elevated flaring events in 2008.
Month Cause of flaring event Quantity of gas to elevated flare
January
February
November
December
2572 tonnes
613 tonnes
2282 tonnes
632 tonnes
Process compressor trip
Valve positioner unplanned maintenance
Gas turbine unplanned shutdown
Gas turbine unplanned shutdown
To date in 2009 the relevant summary of ExxonMobil unplanned flaring events is as given below.
Date flaring Date flaring Quantity of Cause of flaring event started ended gas to elevated flare
18 th May 09 18 th May 09 529 tonnes Acetylene converter trip due to human error
3 June 09 5 June 09 1227 tonnes Sulphinol plant shut down to carry out line repairs.
September figures to be added.
For comparison, it is perhaps helpful to consider the data within the longer-term chart below. This shows the quantities of gas flared for both planned and unplanned events during a period extending from 1994 to the present.
40000
35000
30000
25000
20000
15000
10000
5000
0
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
At the meeting of the Cowdenbeath Area Committee on 2 December it is planned to have short presentations from Wilson Sibbett (Chair, Review Group), Dan O’Connell (ExxonMobil), Michelle
Hickson (SEPA) and Alison Searl (IOM).
Author: Professor Wilson Sibbett is Chair, Mossmorran And Braefoot Bay Independent Air Quality
Review Group.