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BOC Edwards experience in water deaeration equipment spans more than 70 years, serving essentially two markets and applications:
• Seawater deaerators for water injection systems for secondary recovery of oil from offshore reservoirs
• Boiler feedwater and process deaeration for power generation plants, boilers and process use
Seawater deaerators
Secondary recovery by means of water injection is frequently an essential feature of crude oil production. It is often a crucial factor in achieving and sustaining economically viable production rates.
The source of the water is dependant on the location of the production facility and could be from a subsurface source such as produced water or an aquifer, or from a surface source such as the sea or a river. The latter two sources, as with most surface waters, normally contain substantial levels of dissolved oxygen. In order to control corrosion rates in downstream plant and to inhibit bacterial growth this oxygen must be removed before the water is used for injection. BOC Edwards is able to provide extensively proven deaeration technology to facilitate the removal of this oxygen to levels such that the remaining residual may be economically removed by the addition of a chemical scavenger.
The following options are available:
• Spray/pack deaerators
• Packed column deaerators
• Trace gas stripping deaerators
Spray/pack deaerators
Although conventional packed bed deaerators offer a satisfactory solution in many circumstances, the unique BOC Edwards spray packed deaerator technology offers significant advantages over conventional designs. It affords additional benefits for FPSO installations because the mass transfer efficiency of the spray section is unaffected by wave motion and by any foaming of the water as it enters the deaerator.
This patented design offers many benefits over conventional deaerators and compact deaerator designs including the following:
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• Substantial height and weight reduction compared to conventional vacuum stripping columns
• May be used upstream of sulphate reduction membranes, since it can operate without the addition of anti-foam chemicals
• Unaffected by any motion of the installation, making it the preferred technology for FPSO applications
• There is no reliance on catalysts, which have a limited life span and may be poisoned
• There is no requirement for storage and/or production of hazardous combustible products such as methanol or hydrogen
• Extensively field-proven technology, with over 50 units utilizing the spray distributor supplied for water injection service
Packed column deaerators
This conventional design uses well-proven technology and remains the industry standard for both onshore and offshore applications worldwide.
The design is suitable for both vacuum and gas stripping applications with corrosion resistant tower internals designed for foam retention, efficient liquid and gas phase distribution and redistribution, in order to maximize mass transfer efficiency.
Trace gas stripping deaerators
This patented system combines vacuum stripping and inert gas stripping to offer a unit that operates under vacuum with the mass transfer process being assisted by a small quantity of inert gas admitted into the deaerator column. This process allows highly compact deaerator columns to be used whilst the required vacuum pump capacity is substantially lower than would be associated with conventional vacuum stripping deaerators.
Deaeration and the use of sulphate removal systems
BOC Edwards is able to offer field proven designs for water injection deaerators, which are required to operate upstream of sulphate removal systems. Such installations require that the deaerator must operate without antifoam agents since the use of such agents in incompatible with the membranes used in the sulphate removal system.
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BOC Edwards has supplied units to replace conventional packed column deaerator designs supplied by other manufacturers that have proved to be incapable of operating at the required design conditions without the use of antifoam agents. Our ability to offer proven technologies, which provide enhanced mass transfer capability can enable existing deaerator vessels to be re-used in order to minimize the cost and downtime associated with the upgrade.
Sulphate removal systems may be installed upstream of the deaerator in which case antifoam agents may be used, however this location upstream of the deaerator column has many serious disadvantages, which include:
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• Materials of construction of the sulphate removal system must be suitable for service in contact with undeaerated seawater
• Presence of oxygen in the seawater will increase the risk of oxidation of the membranes and/or the possibility of aerobic bacteria or algae growth on the membranes
• Additional precautions to ensure the removal of any hydrocarbons present in the water may be necessary prior to the sulphate removal system to ensure that these do not contact the membranes |
