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Process vacuum

Steam ejector vacuum systems 7-2

Deaeration equipment 7-4

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STEAM EJECTOR VACUUM SYSTEMS

BOC Edwards has over 90 years experience in the design and supply of steam ejector systems. BOC Edwards has been instrumental in the devel-opment of the steam ejector from the relatively crude single stage devices which evolved into today’s highly efficient multi-stage systems.

Process and mechanical design expertise is combined with project manage-ment skills for the supply of individual items of plant, or the execution of total projects including installation and commissioning. The company has an immense reputation in applications including the following: • Refinery Vacuum Systems • Vacuum Distillation Units • Flash Evaporation for Seawater Desalination • Turbine Condenser Air Extraction • Edible Oil Processing • Polymerization • Crystallization • Evaporative Cooling

Features of the steam ejector solution • Low capital cost • No moving parts • Low maintenance • Wide choice of materials • No close clearances • No size limitation • Ability to handle large vapor load • Liquid slugs do not cause mechanical damage • Not sensitive to suction temperature

1 Strainer 5 Diffuser

2 Motive steam 6 Suction

3 Nozzle 7 Vapor Head

4 Discharge 8 Nozzle Holder

RangeEjectors can be arranged as multi-stage systems with interstage condens-ers, which may be the direct contact type (jet condenser) or surface type (shell and tube). The multi-stage arrangements allows lower suction pres-sures to be achieved than could be produced by a single stage ejector. Interstage condensers economize on the use of motive steam, since the operating steam from stages upstream of the condenser is condensed leav-ing only saturated incondensable gases to be handled by the succeeding stage or stages.

Operating pressure Single Stage 150 - 130 mbar

Two Stage 25 - 15 mbar

Three Stage 10 - 7 mbar

Four Stage 1 mbar

Five Stage 0.1 mbar

As ejectors can be economically manufactured on an individual basis to suit specific customer needs they have a wide capacity range, which is limited only by the manufacturing techniques relevant to the material of construc-tion, typically this range would be between 10 - 1.5 x 106 m3h-1.

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Interstage jet condensersJet or spray type condensers operate by condensing steam by direct con-tact with the cooling water. This type of condenser can be located at baro-metric height or at low level using a condensate extraction pump. Jet condensers tend to use less cooling water than surface types, although as the ejected vapors are in contact with the cooling water the treatment of any resulting effluent must be considered.

Interstage surface condensers Surface condensers of the shell and tube type perform the same function as jet types, however the ejector steam and process vapors are condensed on the tube surfaces without contact with the cooling water, greatly reduc-ing the potential effluent problem. Removable end covers on the condens-ers allow easy cleaning of the tubes.

Multistage ejector/liquid ring pump combinations BOC Edwards are able to offer combinations of steam ejectors and liquid ring pumps where the liquid ring pump replaces the final stage or stages of a steam ejector system.

This enables large vapor/gas flows to be handled at the low pressures asso-ciated with multi-stage steam ejector sets whilst substantially reducing steam consumption and hence operating costs.

Ejector and ejector liquid ring pump combinations can be supplied using BOC Edwards designed liquid ring pumps. The depth of experience in both types of equipment allows optimization of the equipment both in perfor-mance and economy of utilities.

Applications and design servicesBOC Edwards offers a comprehensive design service based on unrivalled process vacuum experience, application knowledge and design capabilities.

In order to propose a solution the following information is required at the enquiry stage:• Suction flow • Composition and Molecular weight • Suction pressure • Discharge temperature• System volume• Evacuation time• Discharge pressure • Motive pressure and temperature, max-normal-min • Cooling water temperature, max-normal-min • Type of condenser direct or indirect • Type of installation Barometric or low level • Materials of construction • Design codes applicable

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DEAERATION EQUIPMENT

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 deaeratorsSecondary 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 sub-stantial 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 scav-enger.

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..

1 First stage vapor take-off 4 Recycle

2 Oxygen scavenger 5 Second stage vapor take - off

3 Water outlet 6 Water inlet

This patented design offers many benefits over conventional deaerators and compact deaerator designs including the following: • 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 deaeratorsThis 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 deaeratorsThis 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 with-out 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:• 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

Deaeration on floating production vesselsBOC Edwards has considerable experience in the supply of deaeration packages for use on floating production vessels, including installations on FPSO's, semi-submersibles and on tension leg platforms.

These production facilities require that the deaeration package is insensi-tive to the motion of the installation and that the height and weight of the package together with the elevation of the center of gravity above grade level are minimized.

Our deaeration technology includes designs that are ideally suited to such floating production facilities, with references available for these types of installations at locations around the world, in conditions ranging from off-shore Canada to Equatorial Africa.

Boiler feedwater and process water deaeratorsThe types of deaerator described have been developed over years of expe-rience of the different types required for numerous industrial applications. Examples of some of the industries where deaeration is used are:

Power stations - treating boiler feed water

Oil refineries and chemical plants - treating boiler feed water and process deaeration.

Breweries - deaerating water in the production of high gravity beer.

1 Vent 4 Deaerated water outlet

2 Feed water inlet 5 Off-load Heating Steam

3 Heating steam inlet

High level pressure deaeratorsFor modern industrial installations where heat economy is essential, and where even lower oxygen contents are demanded to avoid costly mainte-nance work, the pressure heater/deaerator system is used where inlet boiler feed water is heated to well above atmospheric boiling point.

BOC Edwards has developed a system of sprays and trays such that the feed water enters the deaerator through an atomizing spray valve assembly into the upper volume of the deaerator vessel where primary deaeration takes place. The feed then falls over a series of trays to the base of the deaerator during the course of which secondary deaeration takes placed.

Heating steam is admitted via a diffuser positioned below the tray assembly to ensure ultimate heating effect and optimum scrubbing action so as to produce residual oxygen contents down to 0.007 p.p.m. or less. This deaerating section is mounted on a storage compartment such that the whole system can be mounted at a suitable height to obtain the required suction head on the boiler feed pump advised by the manufacturer.

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1 Vent 4 Discharge to storage vessel

2 Feed water inlet 5 Balance pipe return

3 Heating steam inlet 6 Manway

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