Learning Objectives
Reduction of the plant cost involved with the basic consideration of case in operation, timely completion of fabrication and erection work, easy access for plant machinery operation and maintenance, safety in plant operation etc. are the basic aims during the conceptualisation of the process plant layout.
The process plant layout is the basic drawing prepared to represent the actual equipment prepared for the actual locations in terms of three space co-ordinates (x, y, z).
It is the drawing prepared at the beginning of any engineering activity and is used for various purposes like civil and structural work, erection of equipment piping instruments, electrical items, etc.
The movement of material, machine and man are a critical consideration during the initial phase of layout preparation. These movements are discussed in this chapter with reference to various activities like plant operations, fabrication and erection, maintenance, safety, economic analysis, aesthetic look, future expansion and geographical factors of any chemical process industry.
I feel that a conceptual understanding of any process plant layout is important not only for the piping designer but also to others professionals involved in the fields like marketing, R & D, process designers, etc.
Introduction
Chemical process industries involve multiple unit processes and unit operations to convert raw materials into products. Different processes as require different types of hardware like equipment, pipelines, instruments etc. Hardware items need space to locate them in process plant building.
Smooth material movements ensure higher process plant productivity. There being a large number of operating steps involved, the proper operating man movement is equally critical for plant performance. Thus the 3 M's viz. materials machine and man are involved in any production process and their smooth movements arte critical for better process plant operations.
Conceptualization of any process plant layout at the early stage is very important. Important facts, if not considered at the appropriate time ma lead to major troubles at a later stage. Following industrial examples elaborates problems caused due to improper process plant layout.
Improper location of equipment increase operational steps. Equipment positioning influence operating steps. For example converting gravity flow to pump flow adds one more step of pump operation.
Insufficient space for insulation. Space not provided for insulation over equipment or pipeline which causes trouble during erection work. This may either be due to insufficient available gaps between two hardware parts or no approach available for laying insulation over these parts.
Poor accessibility if equipment delays plant operations. Discomfort in reaching the faculty equipment causes trouble for taking up any maintenance work. It many times delays plant operations and thus leads to high production losses.
Unsafe handling of hazardous chemicals may harm the plant as well as the operating persons. Hazardous chemical handling requires special attention as they culd be harmful to the life of plant personnel and a danger is plant hardware.
- High cost of land and hardware
If the plant space used is more than the actual required though provides more movement and space, increases the hardware cost in terms of larger amount of piping, civil and structural requirements.
- Haphazardly placed equipment and other hardware generates as unhealthy working environment
Everyone of us likes an aesthetic look to our surroundings. It provides a soothing effect and encourages us towards better performance. Haphazardly placed equipment causes confusion in regular plant operations, which generates more errors.
- The future entry of equipment requires dismantling of the existing equipment structure.
Insufficient space in the existing plant building may be because of erected equipment and piping or building structures like wall, door, etc., causes difficulty for the entry of any new equipment in the future. The expected plant modifications or expansion needs should be considered at the conceptual stage of the process plant layout preparation.
- High rainwater causes operational inconvenience
Process plant equipment located in an open area causes inconvenience to the plant operators during rainy days and thus plant operations are badly affected. The troubles discussed above are some representative cases applicable for any typical chemical process industry.
Major Categories
In General they are Classified into the Following Major Categories:
1. Operations
2. Fabrication and erection
3. Maintenance
4. Safety
5. Economics
6. Aesthetics
7. Expansion
8. Geographical factors
During the preparation of any process plant layout, either for equipment to be fitted in the existing plant building as part of modification or expansion, these points need to be critically viewed.
Operations
Chemical process industries involve multiple operations for the conversion of raw materials to finished products using various types of equipment and other hardware. Though most of the equipment may be operating on its own, manual involvement is required to control their operation. For example the liquid flow rate and the inlet/out valve operations during pump stoppage. The overall plant operations are divided into three categories viz. plant start up, normal plant operation and plant shut down.
The operational points are usually viewed on a priority basic as any trouble in the plant operations directly effect the production. Insufficient elevation differences disturb material flows and cause drying or flooding of the processing system. For example, no distillate draw condition of distillation column causes column flooding and separation efficiency is badly affected.
Fabrication and Erection
Hardware equipment like piping instruments, etc. used in the process industries are either pre-fabricated/procured directly from the market or fabricated at site. Finished or unfinished fabricated materials are moved in position by various available manual or mechanised devices like cranes, monorails forklifts etc.
Likewise along with the material movement and placement, the plant erection contractor is provided with the necessary access to carry out the fabrication and erection work properly.
Maintenance
The process plant handles both static and dynamic equipment, which undergoes maintenance as per the type of equipment and operations. Rotary equipment like pumps, blowers, agitators etc. due to their moving parts, are highly prone to maintenance work as compared to static equipment. Routine maintenance work is preferred to minimise trouble, while emergency maintenance work can't be avoided.
Poor facilities delay maintenance work. Thus the necessary provisions in the plant layout are considered during the conceptualisation of layouts. Poor access to hardware parts also delays the maintenance work. The process plant layout is also critically viewed in terms of maintenance requirements.
Safety
Process plants handle various hazardous chemicals and operations. They demand safety norms, governed by statutory rules and regulations. Run away type reactions, high pressure and temperature operations etc. are critical examples which require safe distances between two-equipment. Fire safety measures, etc. are considered during the preparation of the process plant layout.
Economics
Addition of hardware or land adds up to the cost of the process plant. A rotary unit like a pump adds up to utility cost in the form of electricity every moment. Capital and operating costs play a major role in plant economics. For process plant layout conceptualisation is a major proper concern in minimising the capital as well as operating costs.
Aesthetics
All of us like to work in a pleasent environment. Thus the aesthetic points can't be overlooked. Haphazardly placed equipment gives a bad appearance to the process plant and causes confusion in plant operations, which leads to poor plant performance. Too many pipeline crossings due to improper equipment placement and pipe routings make pipeline tracing difficult and takes away the aesthetic look of the cess plant. Incorrect identification of operating valves leads to wrong opration and even sometimes disastar too.
Expansion
Increase in the process plant capacity requires expansion in terms of its hard ware like reactors, pumps, pipeline instruments, etc. Addition of hardware requires space in process plant as it is built in multiple phases due to various redsons like low market demand for product, low availability of raw material, available capital funds, government clearances, test product launching, Accordingly the plant is also installed in phases. Investment is minimised in the initial phase but necessary provisions are made to minimise cost in terms of hardware and reduced plant stoppages in the later stages. Continuance of new plant expansion with the existing hardware is critical in terms of material flow, movement/maintenance space.
Geographical Factors
Geographical factors indirectly affect the process plant layout. For example, seismically prone areas require more equipment and building foundation space, increasing the land requirements. High rainfall regions are provided with better drainage facility, elevated plinth levels and covered plant buildings, etc.
Material Movement
Material movement starts from its entry at the factory gate in the form of raw material. It passes through various unit processes and operations before it's final conversion to the product. Chemical process industries handle different types of materials in the forms of solids, liquids and gases for raw materials, intermediates and final product streams.
Various points related to materials movements in the process plant layouts are shown in Table 1 and are discussed here.
Plant Operations
Plant operations are broadly categorised into three viz. startup, normal operations and shut down.
Facilities are provided in the process plant to consider these three modes of operations.
The ion exchange column is filled with the resin materials before the start of the plant operation. Additional space is provided near the ion exchange column for unloading resin bags and filling resin materials.
Normal plant operations require a positive flow of materials i.e. a source to the user point. Solids and liquids flow from the high to the low level under gravity. External force is required to transport them from lower to higher level. Pumps and connectors are are conveyors used for this purpose. Fluid flow is critical to plant operations as it directly affects the production process Thus special focus is on these aspects during the process plan conceptualisation.
Sufficient inventory of the raw materials is needed as feed, as process in termediates and as products for some plant operations. Sufficient space is provided in the process plant layout for plant operations and is accommodate material storage maintaining enough inventory level.
The Process plant uses valuable chemicals which can't be lost as in case of any shut down. Thus materials that are intended to be recovered before emptying out the operation system. The necessary elevation and space is provided for the processing units for the easy transfer of the operating system materials into there spective recovery vessels.
Fabrication and Erection Work
Various materials like metal sheet pipelines, valves, structural steel, etc. are required for site fabrication works. Finished materials like pumps, shop fabricated heat exchangers, etc. are directly erected in the process plants or are stored at site before the erection of the site. Fabricated equipment and other hardware materials require movement space, in terms of unloading, lifting, placement, etc., of finished as well as unfinished materials. Additional space like erection bays, cut outs, etc. are considered in the layout to carry out fabrication and erection work. Likewise additional space for the movement of material lifting units like cranes, monorails, forklifts, etc. are considered. Long delivery items are given due considerastionn for their entry, while planning equipment placement.
Maintenance
Harmful chemicals badly affect maintenance personnel. They need to be protected from these harmful chemicals. Equipment handling of such harmful chemicals are emptied out completely before handing over for maintenance. For example concentrated sulphuric acid handing pump is drained fully before offering for any maintenance work. Suitable arrangements like drain and collection arrangements at the lowest points are provided for the safe draining of these hazardous chemicals.
Safety
Flammable and toxic chemical handling demand special attention. Highly flammable chemicals like gasoline, acetone, ethanol etc. are stored in isolated bounded areas with minimum safe distances recommended by safety regulations. Toxic chemicals are stored within a dyke wall area to avoid any accidental damage caused due to the storage tank failure. Approach or internal roads are provided for the safe movement of road tankers carrying hazardous chemicals and fire tenders for emergency operations.
Economics
A compact process plant is preferred to reduce the distances travelled by processing materials. A lower pump head requirement reduces plant-operating cost in terms of electricity power consumption.
Aesthetics
Processing materials are stored and transported in closed systems not only to save losses but for the aesthetic look of the process plant too. Even waste streams are provided with proper concealed piping or gutters. Provisions of such material flow systems are considered in the plant layout.
Expansion
Future plant expansion facilities are considered for material flow. Typical examples are the provision of higher size utility supply and return headers, additional nozzles in the equipment and the piping header with the provision of easy future connectivity etc. Additional space is provided in the pipe rack for laying down future pipeline materials.
Geographical Factors
Some liquid materials have a tendency to freeze at low environment temperature conditions. Thus they require anti-freezing protection facilities like steam or electric heat tracing. Likewise the cooling tower is replaced by chilled water units for locations having very high-wet bulb temperature conditions. High rainfall regions require closed solid storage space.
Machine (Equipment) Movements
Various equipment and hardware are being used in the process industries for carrying out multiple unit processes and operations. They are broadly divided into two-categories viz., static and rotary equipment. Mainly rotary equipment undergoes movement and thus requires more attention. Static equipment like fitter units also need frequent attention for filtered cake disposal, cleaning, etc.
Plan Operations
Identical to the layout provisions for material movements, machine operations are equally critical and need to be understood and to be implemented. For example the appropriate positioning of the push button for pump startup provide operational ease for the operators. Any process plant startup requires equipment cleaning and testing, which requires necessary provisions for utility stations in the plant layout. Continuous operating pumps maintain material flow continuity. Standby units are considered to maintain flow continuity in case of operating unit failure. Cleaning space for units like heat exchangers is provided during plant shut down.
Fabrication and Erection
Space for site fabrication, lifting of the equipment and erection is considered at the preliminary stage of process plant layout. One space required for equipment and pipeline lagging is considered during the conceptualisation of the layout. Some instruments have critical requirements of upstream and down stream straight-line distances for better instrument accuracy, which are achieved by the proper positioning of these instruments in the plant and are considered at the initial stages of layout preparation.
Maintenance
Two types of maintenance works are seen in process plants. Some equipment demands maintenance in place (i.e. taking corrective action only at the equipment location) while in some other cases equipment or instruments are dismantled from their actual position and are taken to the workshop for necessary maintenance work. The first case requires enough space for maintenance persons to carry out work, while the second option demands facilities and provisions like cranes, chain-blocks, floor cutouts, etc.
Safety
Projected parts like nozzles, structural supports, rotary parts, etc. of equipment and machinery causes safety hazard to operators. These parts need to be properly oriented and provided with clear space. Instruments like density measurement units (radio active type) require safe distance and isolation from the operational area. These safer distances are maintained in the process plants.
Economics
Plant cost is substantially reduced by the selection of a compact-layout. If not only reduces land cost but saves piping, civil, structural materials, costs too. Though cost reduction is a wise step, but it should not compromise on other important factors.
Aesthetics
Equipment positioning plays a major role for better looks of the process plant. Systematic laid down equipment like matching centre lines for identical equipment, nozzle orientation and piping, sequencing of equipment as per size etc. improves the aesthetic look of the process plant. Crisscrossing of pipelines is avoided.
Expansion
Space is provided in the process plant building for any future additions of the hardware required for plant expansion. Additional space is reserved for equipment positioning as well as for its entry inside the building area
Geographical Factors
They influence the positioning of equipment. For example, the wind direction guides the location of cooling towers. Flares, furnaces, boilers, spray ponds, etc. Higher equipment foundation sizes are required for poor soil strength as well as for high seismic prone locations. They influence the required distances between equipment too.
Man Movements
Machine do not operate by themselves, man is required to control them. Thus multiple operations are possible only by the operator's involvement. Though the level of automation is making manpower redundant. But absolute elimination is not possible. Man movements within the plant as well as between two plants sections is essentially to be looked at with the various angles specified above.
Operations
Process plants engage multiple equipment, pipelines, valves, instruments to carryout conversion processes. These units need manpower attention for smooth operations. Proper access for measurement, inspection, and control of these units is provided for better plant operations. A plant normally undergoes shut down for two reasons viz, failure or periodic maintenance of plant and machinery or non-availability of raw materials or lower product demand. Either long or short shut downs often demand system cleaning. Space for operators' movements along with maintenance tools for such applications are considered in the layout.
Fabrication and Erection
It requires various operations like cutting, welding, material lifting etc. These operations are carried out manually. Thus space for these operations is considered in the process plant layout. Some erection works also received additional platforms at higher elevations and scaffoldings, which are considered during layout preparation.
Maintenance
Plant maintenance whether in place or carried out in the shop, maintenance days are provided for frequent maintenance works. Necessary access is provided for the maintenance personnel movement near the equipment under maintenance.
Safety
Escape doors are additionally considered for the safe escape of the operating manpower from hazardous locations in the process plant. Safe distances from the rotary units are considered to avoid accidents during the operation and movements in the plant area. Body protection insulation is provided over the hot lines lying in the operational area, where manpower movement is expected. Additional space is considered for the safe movement of operators to avoid high temperature burns Safety railings are considered in the floor cutouts, staircases, etc., for the operating manpower is safe movements in the process plants.
Economics
Various plant operations are combined for reduced manpower operations. Thus a compact layout with positioning of equipment and operating points like valves, instruments etc. is critical for manpower reduction. For example, all the operating pumps can be placed in central pump house so that one operator can start or stop multiple pumps at a time with minimum movement. Remotely dispersed pump locations require many operating personnels. Reduced manpower reduces the operating costs and this improves plant economics. This is especially true for process plants running with a large number of manual operations.
Aesthetics
Human beings by nature to live in neat environment and it effects their performance too. Aesthetic lock of the process plant is important for operating manpower to generate conducive working environment.
Expansion
Process plant expansion also increases the operating manpower requirements. Thus requirement to accommodate and provide the necessary facilities like canteen, rest rooms, parking space etc., for the operating manpower also increases. Along with the expansion of the process plant building, these facilities for manpower are considered in the process plant layout.
Geographical Factors
Manpower movement areas are generally covered to protect them for adverse weather conditions like rainfall, scorching sunlight, high wind velocities etc.
The process plant involves many hazardous chemicals and operations. Thus there is need to safeguard the environment and living beings. Though man is intelligent enough to define the hazard and act to protect himself, many times the high costs involved or sheer negligence causes major havoc. Statutory regulations are made in the interests of protecting the living as well as nonliving entities from these possible hazards. These regulations are mainly derived from the past experiences of handling hazardous chemicals, unit processes and unit operations.
Identical to other parameters, statutory regulations are also categorised here in three parts viz. materials, machines, and man. Material characteristics decide the type of facilities to be provided in the process plant. For example flammable chemicals are isolated for bulk storage and handling, harmful chemical storages are provided with dyke walls for the collection of spilled chemicals or leaked storage tanks, etc.
Hugh distances are maintained for hazardous equipment handling. For example the minimum distance is specified in the regulations for rotary units like pumps, compressors, agitators, etc.
The operational safety of the operators is also governed by statutory regulations. The minimum distances are specified under statutory regulations, which protect operating manpower from any hazard.
Summing Up
Multiple factors have been discussed here for conceptualising process plant layouts. It is often seen that two process plant layouts may not necessarily be identical. Thus every plant needs attention at the conceptualisation stage itself. Looking at the basic requirements, they can be broadly divided into two parts viz. directly visible and hidden requirements. Directly visible requirements, like equipment dimensions, minimum vendor requirements, etc. can be viewed directly and are relatively easy to collect and are used in the process plant layout preparation. Hidden requirements, etc. need the visualisation of the process plant at the early stages of process plant layout preparations.
Tagged as :
Layout Engineering
Piping Design
0 comments :
Post a Comment