Emission control and sealing - finding the best techniques is key
We are all aware that industry as a whole must reduce emissions, and European Union (EU) legislation has developed accordingly. One major item is the Directive on Integrated Pollution Prevention and Control (IPPC), which became mandatory in 2007.Just as with other EU-wide legislation, the Directive has been transposed by EU member states into their own national legislation, which leads to an interesting consequence; in many cases, plant operators and process engineers are oblivious to the IPPC Directive itself. Yet, it is the fundamental 'umbrella' legislation directing the control of emission performance across the entire EU.
The IPPC Directive applies to specific sectors of industry, considered by the European Commission to be the greatest potential sources of industrial pollution. Although most of these industrial categories rely on their supplier sectors - such as the pump, valve and sealing industries - in order to meet compliance, none of these supplier sectors is covered directly by the Directive. Without doubt, we are 'always the bridesmaid, never the bride'.
It is important to recognise that a large proportion of industrial emissions are those anticipated from the processes themselves, under the control of the plant operator, and will not be considered in detail here.
However, a significant portion of industrial emissions occurs through unanticipated or spurious leaks in process systems, often referred to as 'fugitive emissions'. This is an area where sealing technology can play a major role and has been a prime focus of attention for the European Sealing Association (ESA).
Legislation background
The Directive provides an integrated approach for a potential pollutant across all media which might be affected. All industrial installations covered by the legislation must be authorised to operate through a permitting system, based upon the principle of best available techniques (BAT).
This must take into account the industrial sector economics, the technical characteristics of the installation, its geographical location and local environmental conditions. These factors will vary throughout Europe, so it is anticipated that significant differences will emerge in the emission limits and BAT applied by the member states. The Directive recognises this fact, and sets out a procedure for the exchange of information on BAT and emission limits, through a series of so-called BAT Reference (BREF) notes.
In view of this, the European IPPC Bureau was established at the Joint Research Centre in Seville, to assist information exchange on BAT and publish the BREF notes. These were considered initially to be specific for each industrial sector covered by the IPPC regime (so-called, 'vertical' BREF notes). However, it has become apparent that some BAT concepts are applicable across many industrial sectors, and so a series of 'horizontal' BREF notes also has been developed.
In total, 33 BREF notes have been published, of which a number are already under review for updating. The BREF's may be downloaded from the European IPPC Bureau website at http://eippcb.jrc.es/
Sealing industry contribution
In the development of their own BREF notes, the industry sectors covered by the IPPC regime focussed on items of major pollution potential, usually process derived and with little relevance to sealing.
As a result, a number of the early BREF notes had only limited information regarding BAT for sealing technologies. Importantly, a number of new, high integrity sealing solutions have not been considered in detail at all. Yet correct selection and use of the appropriate sealing technology is fundamental in the ultimate reduction of fugitive emissions and the achievement of IPPC compliance.
Such inadequacies in the BREF notes may provide incomplete advice on BAT, especially in relation to sealing technologies. In addition, just like emission monitoring or energy efficiency, sealing technology is involved in virtually all of the sectors covered by the IPPC Directive.
Consequently, on its own initiative, the ESA has developed a 'horizontal' BAT guidance note on sealing technology, as a guideline specifically for industries that fall under the IPPC regulations.
For an industrial sector not covered directly by the IPPC Directive, the sealing industry took a lead in developing this BAT guidance note voluntarily. It is pleasing to report that sections of the ESA document have been incorporated into subsequent BREF notes as appropriate.
ESA BAT guidance note
The ESA document is divided into sectors of equipment found typically at industrial sites that are likely to be covered by the IPPC Directive and provides advice on BAT for sealing technologies used in conjunction with:
- Bolted flange connections.
- Rotodynamic equipment such as pumps and compressors.
- Reciprocating shafts.
- Valves.
In addition, there are sections on generic BAT for sealing technologies, a glossary of sealing terms and conversion factors.
Overall control of fluid loss is essential to the successful operation of mechanical equipment used in fluid handling. Various methods are utilised to control leakage at shafts, rods, or valve stems and other functional parts of equipment requiring containment of liquids or gases.
Modern process equipment with rotating shafts such as pumps and compressors is equipped with gland packings, mechanical seals or 'sealless' systems to eliminate (or at least minimise) emission of the process fluid into the atmosphere. All of these systems require fluid for lubrication; in the majority of arrangements the process fluid is used for this lubrication and a very small level of leakage is inherent.
Pump leaking losses occur mainly where the rotating shaft penetrates the casing. The low leakage levels emitted from pumps and their relatively low numbers in a plant result in the overall leakage contribution from pumps being relatively small. Best available techniques for pumps include:
- Proper fixing of the pump unit to its base-plate or frame.
- Connecting pipe forces to be within those recommended for the pump.
- Proper design of suction pipe work to minimise hydraulic imbalance.
- Alignment of shaft and casing within recommended limits.
- Alignment of driver/pump coupling to be within recommended limits when fitted;
- Correct level of balance of rotating parts.
- Effective priming of pumps prior to start-up.
- Operation of the pump within its recommended performance range. The optimum performance is achieved at its best efficiency point.
- The level of net positive suction head available (NPSHA) should always be in excess of the pump design's net positive suction head required (NPSHR). This can vary, dependent upon the operating position on the pump performance curve.
- Regular monitoring and maintenance of both rotating equipment and seal systems, combined with a repair or replacement programme.
- Exchange gland packings in VOC services for mechanical seals where feasible.
- A selection of appropriate sealing technology based on required maximum leakage control levels and with consideration of process fluid characteristics.
The approach of the European Commission has been to include relative cost details about the best available techniques in every BREF note. Yet for many sealing technologies, the cost of the actual sealing element is infinitesimally small when compared with the investment made in the plant as a whole. Importantly, the unit cost of the sealing technology is overwhelmed completely by the labour costs required to fit the seal, let alone the downtime of the plant. Consequently, in most cases the actual cost of the sealing device is immaterial in terms of economic considerations for BAT.
Despite these reservations, for the sake of completeness, a number of charts are included within the ESA document, in order to provide an overview of the relative cost of the best available sealing technologies versus the environmental impact of the sealing options. For example, the relative life-cycle costs of various pump sealing technologies.
This matrix is intended to be used with typical rotodynamic pumps but cannot be assumed to be universally applicable.
The bubble size reflects population of seal type (hence, general purpose single seals are by far the majority of the installed pump population, whereas gas lubricated dual pressurised seals, being a more recent technology development, are the smallest).
Although often overlooked, the energy efficiency of the particular sealing technology can make the most significant contribution to the life-cycle cost (LCC) overall. In addition, reduced energy efficiency contributes to more emissions at the power generation plant, hence more impact on the environment in considering total emission level. The ESA document contains more detail about LCC analysis and information on the Seal Life-Cycle Cost Estimator tool, developed in conjunction with the US Fluid Sealing Association and accessible from the ESA website.
The ESA Sealing Technology BAT guidance note document is available for download (as a pdf file) from the ESA website at www.europeansealing.com (click on the 'Best available techniques' button on the navigation bar).
In line with the formal BREF notes published by the European IPPC Bureau, the ESA Sealing Technology BAT guidance note will be reviewed on a regular basis and any refinements will be incorporated as necessary, on a three-year cycle provisionally.
- Dr Brian S Ellis is Secretary General of the European Sealing Association, Tegfryn, Tregarth, Gwynedd, UK. www.europeansealing.com. The ESA is a pan-European organisation, established in 1992 and representing a strong majority of the fluid sealing industry in Europe. Its four main aims are: to influence legislation and standards, to provide market information and trends; to raise the profile of the sealing industry; and to provide a discussion forum.
