Plot plan is a primary document in design of a plant. It takes lot of experience, knowledge of international and local standards and regulations as well as Process Flow.
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General Plot Plan Development Philosophy
Block layout should be adopted as far as possible. The entire area should be sub-divided into blocks. If process units are operated in an intergrated way, and shutdowns are taken simultaneously of these units, then they may be considered as single block for interdistances and relative placement purpose.
Plant layout arrangement should follow the general route of raw material to process unit(s) with tankages interposed as required followed by storage & despatch facilities. Blocks should be arranged in sequential order of process flow.
All units and roads should be located on high ground to avoid flooding.
All process units and dyked enclosures of storage tanks shall be planned in separate blocks with roads all around for access and safety. Primary traffic roads in the installation should be outside hazardous areas. Roads separating the blocks shall act as firebreaks.
Pedestrian pathways should be provided / marked alongside the primary traffic roads. Alternative access shall be provided for each facility so that it can be approached for fire fighting in the event of blockage on one route.
Road widths, gradient and turning radii at road junctions shall be designed to facilitate movement of the largest firefighting vehicle in the event of emergency.
Layout of the facilities shall be made to minimise truck traffic ingress in the plant. Two road approaches from the highway / major road should be provided, one for employees and other for product / material movement. Both these approaches should be available for receipt of assistance in emergency.
Roads should be provided in a symmetric manner to serve all process areas requiring access for the operation, maintenance and fire fighting. These roads should encircle the process blocks/ process units.
Main pipe racks / pipe track shall not be routed through process units. Provide overhead clearance for vehicles over roadways and railroads.
Rail spur shall be located close to the periphery of the plant to minimise road/pipe crossings and blockage of roads during shunting. Locate Rail loading facilities along the periphery of the installation
Presence of ignition source shall always be contemplated beyond the boundary wall of the installation.
Located flare stacks upwind of the process units to avoid leaking hydrocarbon vapors reaching flare stack and getting ignited. Area around flare should be paved.
Furnaces and Heaters
Located Fired heaters upwind of process unis to avoid hydrocarbon vapors entering in fired heaters.
Cooling towers shall be located downwind side of process units to avoid fog created by them drift into process units and cause visibility problems as well as corrosion problems. The short side of the tower shall be located into the prevailing summer wind, to accomplish maximum efficiency.
Control room should be located in a non-hazardous area. Control room should be upwind of process plants, hydrocarbon storage and handling facilities. Control room shall not be located at lower level than surrounding plants and tank farms to avoid flooding with process fluids or contaminated rain water. There shall be no structrure that could fall on the control room in case of a blast.
Sulfur handling is a dusty operation. Dust from such operations shall not reach process units. They should be located downwind side of process units. Minimum separation distance of 50 meters is recommended between sulfur storage / handling and any facility or boundary wall.
Equipment drawing air (e.g. air compressors, air blower, FD fan etc) should be located away from Sulfur recovery unit / Sulfur handling facility.
Sulphur recovery unit and sulphur loading area should be located close to product movement gate and away from process units, hazardous and populated areas.
Petrolium Coke Handling
Petroleum coke storage and handling facilities should be located as far as possible away from process units, air separation plants, populated and hazardous areas.
Group storage tanks according to product classification as per relevant national standard. If the area is hilly, locate storage tanks at lower elevations.
If a power generation facility supplies steam to a process block also, locate it near that process block.
When external power grid is interconnected with plant’s own power generation facilities, then either locate the power generation block near the plant boundary or run external power transmission lines underground. Power transmission lines shall never be run above the plant as well as parking areas. Horizontal clearance between power transmission lines and plant shall be as per local electricity rules.
Locate High Tension substations near the major load centers.Locate Low Tension substation in such a way that distance between distance between distribution transformer and farthest motor is minimum.
Fire station, firewater storage & firewater pump house shall be located at a safe place away from hazardous areas. Fire station should be upwind of process units and hydrocarbon storage area with straight approach to process units / other critical areas.
Locate truck loading/unloading facilities close to the product movement gate, and orient in such a way to provide one way traffic pattern for entrance and exit.
Erection methods shall be studied for all types of equipment / structures. Towers, reactors, fired equipment etc should be located in such an area so to facilitate erection.
Locate Utility blocks adjacent to unit blocks.
Effluent Treatment Plants
Separate collection system should be provided for different types of waste generated in the process plant such as oily water, caustic, acid effluents, fecal etc. Effluent Treatment Plant should be located minimum one block away from process unit area, down wind of process units and important areas considering odour & emission of volatile organic compound.
ETP Plant should be closer to disposal point by the side of the boundary and at lower grade to facilitate gravity flow of effluent.
For construction activities, area should be earmarked.
Maintenance requirements for each type of equipment shall be identified and considered.
Future expansion should be assessed and space provision be made accordingly.
Smoking booths should not be provided in the hydrocarbon industry. However if required, these shall be located at minimum distance of 60 meters from any hydrocarbon source.
Relative location of units
Locating unit blocks based on their hazard characteristics, wind direction etc. is a critical activity while developing plot plan. Following rules needs to be adhered to while developing a plot plan.
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