Is a type of layout in which resources are physically grouped by function?

10.2 Plant Layout

Plant layout is a crucial factor in the economics and safety of process plants. Some of the ways in which plant layout contributes to safety and loss prevention (SLP) are:

segregation of different risks,

minimization of vulnerable piping,

containment of accidents,

limitation of exposure,

efficient and safe construction,

efficient and safe operation,

efficient and safe maintenance,

safe control room design,

emergency control facilities,

fire fighting facilities,

access for emergency services,

Security.

Plant layout can have a large impact on plant economics. Additional space tends to increase safety, but is expensive in terms of land, additional piping, and operating costs. Space needs to be provided where it is necessary for safety but not wasted.

The topics considered under the heading ‘plant layout’ are traditionally wide ranging. Topics such as hazard assessment, emission and dispersion, fire and fire protection, explosion and explosion protection, storage and emergency planning are addressed in multiple chapters.

A general guide to the subject is given in Process Plant Layout (Mecklenburgh, 1985). This is based on the work of an Institution of Chemical Engineers (IChemE) working party and expands upon an earlier guide Plant Layout (Mecklenburgh, 1973). The treatment of hazard assessment in particular is much expanded in this later volume. The loss prevention aspects of plant layout have also been considered specifically by Mecklenburgh (1976).

Other work on plant layout, and in particular SLP, includes that of Armistead (1959), R. Kern (1977a–f, 1978a–f), and Brausbacher and Hunt (1993), on general aspects and spacing recommendations; Simpson (1971) and R.B. Robertson (1974a, 1976b)R.B. Robertson (1974a)R.B. Robertson (1976b), on fire protection; Fowler and Spiegelman (1968), the Manufacturing Chemists Association (MCA, 1970/18); Balemans et al. (1974) and Drewitt (1975), on checklists; and Madden (1993), on synthesis techniques.

Plant layout is one of the principal aspects treated in various versions of the Dow Guide by the Dow Chemical Company (1994b). It is also dealt with in the Engineering Design Guidelines of the Center for Chemical Process Safety (CCPS, 1993/13). There are also a large number of codes relevant to plant layout, particularly separation distances and area classification. These are described below.

The treatment given here follows that of Mecklenburgh, except where otherwise indicated. It is appropriate to repeat here, his caution that the practice described should be regarded as typical and that it may need to be modified to account for local conditions, legislation, and established safe practices. In particular, the account given generally assumes a ‘green-field’ site, and some compromise is normally necessary for an existing site.

Selected references on plant layout are given in Table 10.2.

Table 10.2. Selected References on Plant Layout

Cremer (1945); Mallick and Gaudreau (1951); Shubin and Madeheim (1951); Muther (1955, 1961, 1973)Muther (1955)Muther (1961)Muther (1973); McGarry (1958); Armistead (1959); R. Reed (1961, 1967)R. Reed (1961)R. Reed (1967); EEUA (1962 Document 12, 1973 Handbook 7); J.M. Moore (1962); ABCM (1964/3); Dow Chemical Co. (1964, 1966a,b, 1976, 1980, 1987, 1994)Dow Chemical Co. (1964)Dow Chemical Co. (1966a)Dow Chemical Co. (1966b)Dow Chemical Co. (1976)Dow Chemical Co. (1980)Dow Chemical Co. (1987)Dow Chemical Co. (1994); Duggan (1964a); Jenett (1964c); Landy (1964a–c)Landy (1964a)Landy (1964b)Landy (1964c); Risinger (1964i); R. Wilson (1964b); Liston (1965, 1982)Liston (1965)Liston (1982); IP (1980 Eur. MCSP Pt 2, 1981 MCSP Pt 3, 1987 MCSP Pt 9, 1990 MCSP Pt 15); R. Kern (1966, 1977a–g, 1978b)R. Kern (1966)R. Kern (1977a)R. Kern (1977b)R. Kern (1977c)R. Kern (1977d)R. Kern (1977e)R. Kern (1977f)R. Kern (1977g)R. Kern (1978b): M.W. Kellogg Co. (1967); BCISC (1968/7); Fowler and Spiegelman (1968); Kaltenecker (1968); House (1969); Proctor (1969); British Cryogenics Council (1970); J.R. Hughes (1970); ICI/RoSPA (1970 IS/74); Kaess (1970); Sachs (1970); Tucker and Cline (1970); Bush and Wells (1971, 1972)Bush and Wells (1971)Bush and Wells (1972); Simpson (1971); Guill (1973); Mecklenburgh (1973, 1976, 1982, 1985)Mecklenburgh (1973)Mecklenburgh (1976)Mecklenburgh (1982)Mecklenburgh (1985); Pemberton (1974); R.B. Robertson (1974a,b, 1976a,b); Unwin, Robins and Page (1974); Falconer and Drury (1975); Beddows (1976); Harvey (1976, 1976b); Spitzgo (1976); Rigby (1977); Kaura (1980b); Kletz (1980h, 1987c); F.V. Anderson (1982); O’shea (1982); Goodfellow and Berry (1986); Brandt et al. (1992); Meissner and Shelton (1992); Bausbacher and Hunt (1993); Madden (1993)Madden (1993); Briggs (1994) ANSI A, A10, A37 and D series, BS 5930: 1981Layout techniquesMecklenburgh (1973, 1976, 1985); Sproesser (1981); Nolan and Bradley (1987); Madden, Pulford and Shadbolt (1990); Madden (1993)Virtual reality: IEE (1992 College Digest 92/93)Civil engineering, including foundationsASCE (Appendix 27, 28Appendix 27Appendix 28); Urquhart (1959); Biggs (1964); ASTM (1967); Macneish (1968); Benjamin and Cornell (1970); Tomlinson (1980); Carmichael (1982); M. Schwartz (1982a–c, 1983a–e, 1984)M. Schwartz (1982a)M. Schwartz (1982b)M. Schwartz (1982c)Mecklenburgh (1983a)Mecklenburgh (1983b)Mecklenburgh (1983c)Mecklenburgh (1983d)Mecklenburgh (1983e)Mecklenburgh (1984); Pathak and Rattan (1985); Blenkinsop (1992); BS (Appendix 27 Civil Engineering, Construction), BS 6031: 1981, BS 8004: 1986, BS COP 2010: 1970–, BS COP 2012: 1974–Equipment weights: El-Rifai (1979)Hazardous area classification (see Table 16.2)Materials handlingWoodley (1964); Smego (1966); R. Reed (1969); Department of Employment and Productivity (1970); Brook (1971); DTI (1974); Pemberton (1974); Sussams (1977); Chemical Engineering (1978b)In-works transport, roadsHSE (1973 TON 44); Mecklenburgh (1973, 1985); HSE (1985 IND(G) 22 (L); 1992 GS 9)Separation distancesC.W.J. Bradley (n.d., 1985); Armistead (1959); Dow Chemical Co. (1964, 1966a, 1976, 1980, 1987, 1994)Dow Chemical Co. (1964)Dow Chemical Co. (1966a)Dow Chemical Co. (1976)Dow Chemical Co. (1980)Dow Chemical Co. (1987)Dow Chemical Co. (1994); Scharle (1965); Home Office (1968/1, 1971/2, 1973/4); Masso and Rudd (1968); Goller (1970); J.R. Hughes (1970); ICI/RoSPA (1970 IS/74); Laska (1970); Simpson (1971); OIA (1972 Publication 631); HSE (1973 HSW Booklet 30); Mecklenburgh (1973, 1976, 1985)Mecklenburgh (1973)Mecklenburgh (1976)Mecklenburgh (1985); Unwin, Robins and Page (1974); Butragueno and Costello (1978); IP (1980 Eur. MCSP R 2, 1981 MCSP R 3, 1987 MCSP R 9); API (1981 Refinery Inspection Guide Chapter 13, 1990 Std 620, 1993 Std 650); Nolan and Bradley (1987); D.J. Lewis (1989b); Martinsen, Johnsen and Millsap (1989); NFPA (1989 NFPA 50A, 50B, 1992 NFPA 58, 59); IRI (1991, 1992)IRI (1991)IRI (1992); LPGLTA (1991 LPG Code 1 Pt 1)Control roomsBradford and Culbertson (1967); Burns (1967); Prescott (1967); Schmidt (1971); E. Edwards and Lees (1973); Mecklenburgh (1973, 1976, 1985)Mecklenburgh (1973)Mecklenburgh (1976)Mecklenburgh (1985); V.C. Marshall (1974, 1976a,c,d)V.C. Marshall (1974)V.C. Marshall (1976a)V.C. Marshall (1976c)V.C. Marshall (1976d); Kletz (1975e); Anon. (1976 LPB 11, p. 16); Gugan (1976); Harvey (1976, 1976b); Langeveld (1976); Anon. (1977 LPB 16, p. 24); Balemans and Van De Putte (1977); CIA (1979); Cannalire et al. (1993)Emergency sheltersJohnston (1968); Lynskey (1985)Indoor plantsR. Kern (1978a); Munson (1980)StorageFPA (1964/1); IP (1980 Eur. MCSP R 2, 1981 MCSP R 3, 1987 MCSP R 9); Home Office (1968/1, 1971/2, 1973/4); J.R. Hughes (1970); ICI/RoSPA (1970 IS/74); HSE (1973 HSW Booklet 30); Wirth (1975); Hrycek (1978); D.W. Johnson and Welker (1978); Aarts and Morrison (1981); NFPA (1986 NFPA 43C, 1989 NFPA 50A, 50B, 1990 NFPA 43A, 50, 59A, 1992 NFPA 58, 59, 1993 NFPA 43B); LPGITA (1991 LPG Code 1 R 1)Fire prevention and protectionFPA (CFSD FPDG 2); IRI (1964/5); BCISC (1968/7); IP (1980 Eur. MCSP R 2, 1981 MCSP R 3, 1987 MCSP R 9, 1993 MCSP R 19); Home Office (1974– Manual of Firemanship); J.R. Hughes (1970); ICI/RoSPA (1970 IS/ 74); Simpson (1971); Mecklenburgh (1973, 1976, 1985)Mecklenburgh (1973)Mecklenburgh (1976)Mecklenburgh (1985); R.B. Robertson (1974a,b, 1976a,b)R.B. Robertson (1974a)R.B. Robertson (1974b)R.B. Robertson (1976a)R.B. Robertson (1976b); Klootwijk (1976); Kaura (1980a)DrainsJ.D. Brown and Shannon (1963a,b)J.D. Brown and Shannon (1963a)J.D. Brown and Shannon (1963b); Seppa (1964); ICE (1969); Mecklenburgh (1973, 1976, 1985)Mecklenburgh (1973)Mecklenburgh (1976)Mecklenburgh (1985); Klootwijk (1976); Anon. (1978 LPB 19, p. 10); Elton (1980); Gallagher (1980); D. Stephenson (1981b); Easterbrook and Gagliardi (1984); Mason and Arnold (1984); Chieu and Foster (1993); Crawley (1993 LPB 111); BS 8005: 1987–Barge mounted and ocean-borne plantsBirkeland et al. (1979); Charpentier (1979); Glaser, Kramer and Causey (1979); J.L. Howard and Andersen (1979); Jackson (1979); Jansson et al. (1979); Shimpo (1979); Ricci (1981); H.R. James (1982); De Vilder (1982)Plant identificationNFPA (1990 NFPA 901); API (1993 RP 1109); BS (Appendix 27 Identification of Equipment), BS 1710: 1984, BS 5378: 1980–Hazard assessmentMecklenburgh (1982, 1985)Mecklenburgh (1982)Mecklenburgh (1985)

14.8 Safety Considerations in Plant Layout

Plant layout is often a compromise between a number of factors, including safety aspects such as (Brandt et al., 1992; Meissner and Shelton, 1992):

The geographical limitations of the site.

The distances for transfer of materials between plant and storage units to reduce costs and risks.

Interaction with existing or planned facilities on site such as existing roadways, drainage and utilities routings.

The spaces for plant operability and maintainability.

The hazardous and flammable material storages.

Emergency services and escape routes for on-site personnel.

The need to provide acceptable working conditions for operators.

Preventing and/or mitigating the escalation of adjacent events (domino effect).

Ensure that safety within on-site and off-site occupied buildings is maintained.

Controlling the access of unauthorised personnel.

Hazard assessment of site layout is critical to minimise consequences of loss of containment and chances of escalation. The Domino effect may be by fire, explosion or toxic gas cloud causing loss of control of operations in another location.

The spread of fire from its origin to other parts of the premises can be prevented by vertical and horizontal compartments using fire-resisting walls and floors. Consideration should also be given to the spread of flammable material via drains, ducts and ventilation systems. Delayed ignition following a release may result in the spread of flames.

Protection against domino effects by convection, conduction and radiation can be achieved by inherent safety principles, that is, ensuring that the distances between plant items are sufficient to prevent overheating of adjacent plants, therefore compromising the safety of those plants. Where this is not possible due to other restrictions, other methods, such as fire walls and active or passive fire protection, may be considered.

Plant Layout design techniques applicable to the reduction of the risks from release of flammable or toxic materials include:

Locating the storage of flammable/toxic material outside process areas.

Locating hazardous plants away from main roadways through the site.

Fitting remote-actuated isolation valves where high inventories of hazardous materials may be released into vulnerable areas.

Allowing for the provision of dykes and sloping terrain to contain releases, increase the safety and reduce environmental effects.

Siting of plants within buildings as secondary containment.

Siting of plants in an open air environment to ensure rapid dispersion of minor releases of flammable gases and vapours and thus prevent concentration build-up which may lead to flash fires and explosions.

Hazardous area classification for flammable gases, vapours and dusts to designate areas where ignition sources should be eliminated.

Figure 14.4 shows typical refinery layout based on the above instructions for minimising risks. The distance between occupied buildings and plant buildings will be governed by the need to reduce the dangers of explosion, fire and toxicity. In particular, evacuation routes should not be blocked by poor plant layout, and personnel with more general site responsibilities should be housed in buildings sited in a non-hazard area near the main entrance. Consideration should be given to the siting of occupied buildings outside the main fence. In all cases occupied buildings should not be sited downwind of hazardous plant areas.

B Plantwide Productivity

In contrast to high task-level productivity, plantwide efficiency measured by unit input requirements of labor, equipment, and materials is generally reported to be low.

Plant layout and scheduling have a substantial effect on productivity. In many machine-producing activities, neither the order of operation nor the placement of machines is inherent in the process. Nor is it physically difficult simply to stop the process and hold a partly finished piece at a workstation until it is again convenient to work on it. Although the inefficiencies generated by the wide latitude of choice could be solved by adequate management, the detailed studies of plant operations in LDCs demonstrate that this is not the case. The typical plant exhibits a poor layout, in which the movement of work in process interferes with operations at individual workstations, where an accumulation of partly finished pieces is held until workers return to them. And despite the fact that the diversity of products requires careful scheduling to increase the use of equipment, all of the studies report poor scheduling. Thus the productivity of both labor and equipment are decreased, and the substantial work-in-process inventory generates interest charges that are higher than necessary.7

5.1 Introduction

Plant layout can affect the total operation of a company, including the production processes, equipment, storage, dispatch and administration. It has a direct effect upon production efficiency and economics of the operation, the morale of employees and can affect the physical health of operatives.

A production facility will be considered as a facility for processing pharmaceuticals or food products or manufacturing engineering products or consumer goods. The facility must utilize real estate, equipment, materials and labour to generate profit for investors and, philosophically, to enrich the life of all associated with it.

Layout planning involves knowledge of a wide range of technologies that will extend beyond those of individual planners and the full range of expertise may not exist in a production facility. Consultants can provide the expertise but guidance can be found in the published works listed in the References

The design methods presented here allow a layout plan to be quickly formulated. The methods rely upon a thorough understanding of factory operations gained from experience and a good understanding of the relationship between people and equipment. When such an understanding is not present a more rigorous approach is recommended. Muther1 published a formalized procedure in 1973 and Tompkins and White2 a more academic method in 1984, both valuable contributions to problems of layout planning.

The first step in any design is to identify the real need, and this is often the most difficult task. Without it, designs can be produced which do not satisfy the requirements and the end result is often unsatisfactory. It is essential to clearly define the objectives of the task and to re-confirm the objectives as time progresses. A useful aid is a value analysis at the end of the concept design stage. This assesses the design for value for money while meeting the defined project objectives. A good source document is A Study of Value Management and Quantity Surveying Practice, published by The Royal Institute of Chartered Surveyors.

A criterion of effective plant operation used to be efficient utilization of capital equipment. The main requirement is now recognized as short door-to-door times, not short floor-to-floor times. The prime need is therefore to achieve a plant layout which facilitates reception of raw materials and dispatch of finished goods in the shortest possible time with minimum capital tied up in work in progress (WIP). This involves access to the site, reception of goods vehicles, raw material goods storage and issue to production, procurement of component parts and sub-assemblies from sub-contractors, process technology and process routes, integrating the sub-contractors’ supplies, finished goods storage and dispatch to the customer.

5.3 The Project Life Cycle

Plant layout is a subset of process plant design, which itself fits into the wider background of an overall project life cycle. The details of project life cycles vary between industries, but there is a common core. Take, e.g., the life cycle for a pharmaceutical project:

Identify the problem (a stage frequently overlooked if there is an assumption that the problem has already been defined)

Define the problem in business, engineering, and science terms

Generate options that provide potential solutions to the problem

Review the options against predetermined selection criteria and eliminate those options that clearly do not meet the selection criteria

Generate the conceptual process design for the selected options

Commence FEED studies. In parallel:

Commence development work at the laboratory scale to provide more data to refine the business, engineering, and science basis of the options

Commence a FEED study to evaluate the possible locations, project time scale, and order of magnitude of cost

Develop the business case at the strategic level

Determine regulatory requirements for product/process

Based on the outcomes of Step 6, reduce the number of options to those carried forward to the next level of detail

Commence Detailed Design. In parallel:

Continue the development work at the pilot plant scale

Based initially on the data from the laboratory scale, develop the detailed design of the remaining options to allow a sanction capital cost estimate to be generated and a refined project time scale

Continue to develop the business scale leading to a project sanction request at the appropriate corporate level

Based on the outcomes of Step 8, select the lead option to be designed and installed

In parallel:

Continue the development work at the pilot scale

Carry out the “design for construction” of the lead option. A “design freeze” will almost certainly need to occur before the development work is complete

Construct the required infrastructure, buildings, etc. and install the required equipment

Commission the equipment

Commission the process and verify that the plant performs as designed and produces product of the required quality, validate

Commence routine production

Improve process efficiency based on the data and experience gained during routine production

Increase the plant capacity making use of process improvements and optimization based on the data and experience gained and revalidate

Decommission the plant at the end of the project life cycle.

The pharmaceutical sector tends to run more stages in parallel than other sectors but most of these stages exist in all sectors. The emboldened text above represents the consensus stages of the process.

Where does plant layout fit into this? Consultants might define Stages 1–3 above as plant design. Those with a background in EPC usually consider design as being predominantly what those in operating companies call “grassroots design,” broadly Stages 3–10 above. Those working within operating companies might also, however, consider Stages 15 and 16 to be plant design.

For the purposes of this book, the project life cycle will be divided into the following five stages:

Stage 1: “Conceptual” Design (broadly Stages 1–5 of the list above)

Stage 2: “Front End Engineering” Design (Stages 6 and 7)

Stage 3: “Detailed” Design (Stages 8 and 9)

Stage 4: “For Construction” Design (Stages 10 and 11)

Stage 5: “Post Construction” Design (Stages 12–17)

Fig. 5.1 illustrates how these activities fit together on an illustrative Gantt chart.

There are many other ways to split the design process up, and these terms may be used by others to mean different things, but the above definitions have been applied consistently in the main text of this book. In Appendix D, however, there are nine common variants on this approach.

Although it is shown as a single bar in the chart, the production of the various deliverables is repeated at least once in each of the stages of design for the duration shown. Blue activities are those outlined in the project life cycle shown above, with some common linking activities shown in green. Process deliverables are in gray, layout deliverables in light blue, and safety deliverables in red.

1 Introduction

The process plant layout problem involves decisions concerning the spatial allocation of equipment items and the required connections among them (Mecklenburgh, 1985). Increased competition has led contractors and chemical companies to consider these decisions during the design or retrofit of chemical plants. In general, the process plant layout problem may be characterised by a number of cost drivers such as connection, land area, construction costs, as well as management/engineering issues (for example production organisation). So far, safety aspects are considered in a rather simplified way by introducing constraints with respect to the minimum allowable distance between specific equipment items. However, it is evident that there is a need for considering safety aspects in more detail within process plant layout and design frameworks.

A number of different approaches have been considered for the process plant layout problem including graph partitioning for the allocation of units to sections (Jayakumar and Reklaitis, 1994) and a grid-based, mixed integer linear programming (MILP) model based on rectangular shapes (Georgiadis et al., 1997). Continuous domain MILP models have recently been suggested, determining simultaneously orientation and allocation of equipment items (Papageorgiou and Rotstein, 1998), utilising a piecewise-linear function representation for absolute value functionals (Ozyruth and Realff, 1999) and considering irregular equipment shapes and different equipment connectivity inputs and outputs (Barbosa-Povoa et al., 2001).

Particular attention to safety aspects of the process plant layout problem was given by (Penteado and Ciric, 1996) proposing an MINLP model. A heuristics method has been described by Fuchino et al. (1997) where the equipment modules are divided into subgroups and then sub-arranged within groups according to safety. Finally, the plant layout problem utilising safety distances, has been solved efficiently by using genetic algorithms (Castel et al., 1998).

This work aims at extending previous continuous domain process plant layout models to include safety aspects using mathematical programming.

2 An overview of Fertec

The plant layout of Fertec A is shown in Figure 1 indicating the location of the main process areas and the maintenance resources (labor and parts store). The labor resources are identified by a letter code that carried through to the organizational models (not shown).

An outline process flow diagram is shown in Figure 2. The ammonia plant is production critical since it supplies the other plants with ammonia and CO2. There is some inter-stage ammonia storage. The plant can also be supplied with imported ammonia, which is much more expensive than that produced internally.

The complex is some 30 years old but has been up-rated especially in the areas of instrumentation and control systems. The urea plant is currently being up-rated. The cost of energy (natural gas) is a very high percentage of the ammonia-plant-operating cost. The energy efficiency of the ammonia plant is low compared to the worlds best because it has ‘old technology’. The reliability of the plant has a major influence on energy efficiency and needs to be improved.

Fertec Ltd is one of a number of companies that belong to the parent group Cario Ltd. The senior management structure of Fertec A Ltd and its relationship with Fertec B Ltd, and its parent group is shown in Figure 3. It should be noted that the Reliability Manager has responsibilities that cover both Fertec Plant A and Fertec Plant B.

A number of the senior positions in Fertec A had recently changed and had been filled with a young forward-looking team. The new team commissioned the audit because they felt that in order to remain competitive they needed to improve plant reliability and at the same time reduce maintenance costs.

Layout Considerations

The plant layout designer, with input from the design engineers, determines the piping layout using common sense, his or her knowledge of how the plant operates and the way the equipment is maintained, and certain general principles to arrive at an optimum configuration that meets the client's requirements, standards, and specifications. The objective of the layout designer is to create a safe, functional, and cost-effective layout.

Input to the layout process is obtained from engineers of all disciplines, including process, civil, structural, vessel, project, mechanical, furnace, exchanger, rotating equipment, instruments, electrical, inspection, and construction. It is at this juncture that the machinery reliability professional will again address such issues as accessibility, maintainability, and surveillability. Surely, an inappropriate equipment layout could present a serious impediment to achieving one or more of these key ingredients of a reliable machinery installation.

As a first step in-plant layout, the location of all equipment on the plot plan is determined. The questions of sequence of construction, handling of large pieces of equipment, operability, maintenance, and economics need to be addressed. As an example, a very large vessel may need to be manufactured and installed in two pieces, welded together in the field, and the weld pressure-tested. Parts of the surrounding structure may be erected last to leave room for the installation of the large vessel.

The locations of all nozzles required for process, utility, and instruments are then determined on the plan, and finally safety and miscellaneous items are located before the piping layout begins. The piping layout is best done on the basis of treating the unit as a whole, rather than locating one line at a time.

The inlet line of a centrifugal compressor is designed with a minimum of three pipe diameters of straight run between the inlet nozzle and the first elbow. Preferably, the horizontal run is parallel to the compressor shaft. Strainers are installed between the block valve and the inlet nozzle. All lines that must be removed for maintenance are flanged. All operating valves must be accessible.

Line design should be simple and close to the ground for easier support. Supports can be on individual foundations, separate from the compressor foundation, to minimize the transmission of piping vibrations. This may not be desirable however where soil conditions make it difficult to control differential support settlement. In that case, the support should be put on the same foundation as the compressor, because differential support settlement can be more detrimental to the piping.

Pump piping may include large expansion loops for needed flexibility. Pump nozzle allowable loads are very low, and care must be taken to avoid overstressing the pumps. Overstressing will not only void the pump manufacturer's warranty, but may lead to internal misalignment and high failure rates in mechanical seals and bearings. This is an important issue which will be addressed in more detail later.

To keep pump nozzle loads within manufacturer's allowable, the piping must be properly supported. The need to remove the pumps for maintenance must be taken into account. The piping configuration is often duplicated for various groups of pumps of the same size under similar service conditions, i.e. a standard pump layout is used. Multiple pump piping arrangements should be such as to minimize the support requirements. Refer to Figures 18-1 and 18-2 for typical pump suction and discharge piping arrangements, respectively.

Figures 18-3 and 18-4 illustrate additional piping-related requirements that must be verified on pump layouts. Because turbulent flow through valves may adversely affect pump reliability, prudence requires valves to be located a sufficient distance from the suction nozzle. This is especially important where double-flow pumps are concerned (Fig. 18-3). Similarly, elbows should be located at least five pipe diameters away from the pump suction nozzle. The effect of not having at least five diameters of straight run between elbow and nozzle is shown in Figure 18-4.

Steam turbine piping is laid out with the steam trap at the low point of the system in order to avoid the introduction of steam condensate into the turbine case and the resulting blade damage.

2.2 Operation and performance characteristics

The plant layout is much the same as that for conventional PHES, except that the high-density fluid (HDF) is transferred between tanks, rather than open reservoirs. The system is based on familiar reversible pump-turbines, designed for use with HDF (there are significant differences between a 200 m head HDF turbine and a 500 m head water turbine of the same rating).

Use of HDF introduces specific O&M requirements. The fluid is a water-based suspension of multiple components. It is nontoxic, environmentally benign, nonreactive, and noncorrosive. It is stable enough to remain idle for 2–3 weeks, if there are periods when plant operation is not required (after which, the clock can be “reset” by circulating ∼20% of the fluid volume through the HDF management subsystem). If necessary, the fluid can be dewatered and kept stable for months—for example, during a major refurbishment or upgrade.

HDF is more abrasive than water, which would shorten the working life of key components (e.g., the pump-turbine) if the same specification were used as for a water-based system. In practice, the specification can be altered to provide an appropriate balance between capital and operating costs. A closed-loop HDF system is highly predictable and so remedial work forms part of the planned maintenance schedule. It is expected that the interval between the replacement of wearing parts (at <2% of the original project cost) will be typically about 17,500 operating hours. Unlike a grid-scale battery with similar operating life, performance can be restored and the cycle repeated to achieve a total operational design life of around 175,000 operating hours.

Overall HDF performance characteristics are similar to those of conventional PHES, which may indicate a rough balance between the advantages of higher density and the disadvantages of a fluid with viscosity similar to a light vegetable oil (the development program includes plans to reduce tHDF viscosity from around 35 cP to 20 cP). Round-trip efficiency is expected to exceed 80% (∼83% for larger projects in the company's range). The core business area is expected to cover projects from 10 MW to 50 MW, with 2–12 h of storage capacity.