Food Processing Plant Design & Layout

Lesson 8. Layout Design Procedure

• The material factor: includes design, variety, quantity, the necessary operations, and their sequence.

• The main factor: includes direct workers, supervision and service help, safety and manpower utilization.

• The machinery factor: includes the process, producing equipment and tools and their utilization

• The movement factor: includes inter and intradepartmental transport and handling at the various operations, storage and inspection, the materials handling equipment.

• The waiting factor: includes permanent and temporary storage and delays and their locations.

• The service factors: include service relating to employee facilities such as parking lot, locker rooms, toilets, waiting rooms etc.; service relating to materials in terms of quality, production control, scheduling, dispatching, waste control; and service relating to machinery such as maintenance.

• The building factor: includes outside and inside building features and utility distribution and equipment.

• The change factor: includes versatility, flexibility and expansion

Each of the above mentioned factors comprise a number of features and the layout engineer must review these in the light of his problem. Usually the layout design process is a compromise of these various considerations to meet the overall objectives in the best possible manner.

The overall layout design procedure can be considered to be composed of four phases Viz.,

Phase I: Location

Phase II: General Overall Layout

Phase III: Detailed layout

Phase IV: Installation

Some important guidelines that help in the layout design are:

• Plan from whole to details

• First plan the ideal and then move to the practical aspects

• Material requirements should be central to the planning of process and machinery.

• modify the process and machinery by different factors to plan the layout

• Though there is always an overlap in the different phases of layout design the major steps that have to be followed in the layout design are outlined as follows:

• state the problem in terms of its objective, scope and factors to be considered

• Collect basic data on sales forecasts, production volumes, production schedules, part lists, operations to be performed, work measurement, existing layouts, building drawing etc.

• Analyze data and present it in the form of various charts

• Plan the production process and its arrangement

• Plan the material flow pattern and develop the overall material-handling plan

• Estimate plant and machinery requirements Select material handling equipment

• Determine storage requirements

• Design and plan activity relationships

• Plan auxiliary and service facilities including their arrangement

• Determine space requirements and allocate activity areas

• Develop plot plan and block plan i.e. integrate all plant operations

• Develop detailed layouts and plan building along with its arrangement

• Evaluate, modify and check the layouts

• Install layouts and follow up

The Systematic Layout Planning (SLP) procedure as presented by Francis and White (1974) is shown in Figure 8.1. We see that once the appropriate information is gathered, a flow analysis can be combined with an activity analysis to develop the relationship diagram. Space considerations when combined with the relationship diagram lead to the construction of the space relationship diagram. Based on the space relationship diagram modifying considerations and practical limitations, a number of alternative layouts are designed and evaluated.

8.1 Data collection

The development of any layout is dependent on the quality and quantity of facts that we have about the various factors influencing it. The data collection phase is not a one-time effort but an ongoing function. The data for overall plan is to be collected at initial stages where as the data for detailed layouts may be obtained at a later stage, the facts have to be obtained regarding various materials and processes, the flow routing and sequencing, space requirements and different activities and relationships.

Figure 8.1 Systematic layout planning procedure

8.2 General guidelines / considerations 

8.2.1 Site layout:

A good site layout provides safe and economical flow of materials and personnel. A material sheet for the site is therefore prepared which then allows the various processes to be positioned relative to one another. The services (e.g. boiler house, effluent plant etc.) are then added in the most convenient positions. The central buildings (administration, canteen, laboratories etc.) are placed in such a manner that the distances traveled by personnel to use them are minimized. Finally the road and rail systems are marked in. Typical sizes and clearances for the site layout are given in Tables 8.1 to 8.3. Having established site constraints and standards, a more detailed site layout can be made. The site layout thus prepared should then be considered to see whether the layout is consistent with safety requirements and that it assists action in any emergency as also the constraints and standards have not been violated.

Broad guidelines for preparation of the site layout are given below:

• Minimize the distance that materials have to travel to or from stores or during processing

• Separate the raw material unloading and finished product loading facilities

• Isolate the hazardous operations

• Locate storage areas close to unloading and loading facilities

• locate boiler room, power station, cooling towers, water pumping station etc. on periphery but adjacent to the area of largest use

• The usual clearances between pipes including flanges and lagging and between pipes and other objects should be 25 mm but this should be increased if hot pipes run near plastic pipes, cables etc.

• Steam and water mains, electricity and telephone cables etc. should, in general, run parallel to the road system and should avoid going through plant area

• Locate office building close to the main entrance

• Provide adequate parking facilities for vehicles waiting to load / unload, cars, scooters etc.

• Plan roads in such a manner that the vehicles do not pass through process areas. Ideally, outside of a plant should be accessible on all four sides by road

• Workshop and general stores should be located within easy access of the processing units.

Table 8.1 Typical clearances between various units for preliminary site layouts

Area	To	Clearance, m
Plant areas	To the adjacent unit, main roads or boundary	15
Boilers and furnaces		15
Blow down stacks with flares		30
Gas holders		30
Cooling towers		30
Effluent plants		15
Loading areas	To process units	15
Ware houses		30
Offices and canteens		30
Medical center		30
Garage		30
Fire station		30
Work shops		30
Main roads		12
Main roads	To building line excluding loading bays	9
		15
		15
Roads	Center line to loading bay head room	7
Paved areas and paths		4
Rail roads		5

 

Table 8.2 Typical areas and sizes for preliminary site layouts

Administration	10 m2	per administration employee.
Work shop	20 m2	per workshop employee
Laboratory	20 m2	per laboratory employee
Canteen	1 m2	per dining place
	3.5 m2	per dining place including kitchen and store
Medical center	0.1 - 0.15 m2  10 m2 minimum	per employee depending on complexity of service
Fire station (housing 1 fire, 1 crash, 1 foam, 1 generator and 1 security ,vehicle)	500 m2	per site
Garage (including maintenance)	100 m2	per vehicle
Main roads	10 m	wide
Side roads	7.5 m	wide
Pathways	1.2 m	wide upto 10 people /minute
	2 m	wide for 10 people / minute (near offices, canteen etc.)
Road turning circles	900 turn	11 m radius
	T junction	7.5 m radius
	minor roads	4 m radius
Minimum railroad curve	56 m	inside curve radius
Cooling towers per tower	0.04 m2/ kWh	mechanical draught
	0·08 m2 / kWh	natural draught

 

Table 8.3 Typical constraint allowances for preliminary plant layout

Equipment	Safety	Horizontal	Vertical	Construction/ Erection/ General
Centrifuges Crushers Mills		3 m	2 m + L	5 m access corridor
Dryers		1.5 m + L	2 m + L	2.5 m to building
Columns		1.5 m		3 m between adjacent columns
Furnaces and fired heaters	15 m to hazard	3 m		2 widths (center to center adjacent heaters )
Reactors Stirred vessels	15 m to hazard	1.5 m	3 m + L	4 m access area 40 m2for each 30 cm3 reactor volume
Heat exchanger (horizontal)		1.5 m +I channel 1.5-2 m shell side	1.5 m
Tanks	15 m to hazard	1/2 dia (avg.) between tanks	3 m
Pumps		2 m motor end 1.5 m sides
Filters		1.5 m + L
Compressors		1.5 m + L	3 m + L	2 widths (center to center adjacent compressors )

L: is the length of the longest internal part of the equipment that must be removed for maintenance or operation.

8.2.2 Plant layout

In general, a most economical plant layout is that in which spacing of the main equipment items is such that it minimizes the interconnecting pipe work and structural steel work. As a general rule, layout should be as compact as possible with all equipment at ground level and it should conform to access and safety requirements. The major considerations are listed below:

Equipment should be laid to give maximum economy of pipe work and supporting steel. Normally, they should be laid out in a sequence to suit the process flow, but exceptions to this arise from the desirability to group certain items such as tanks or pumps or perhaps to isolate hazardous operations.

In general, high elevation should only be considered when ground space is limited or where gravity flow of materials is desired.

Equipment items which are considered to be a source of hazard should be grouped together and wherever possible should be located separately from other areas of the plant.

Provide sufficient clear space between critical and mechanically dangerous or high temperature equipment to allow safety of operating or maintenance personnel.

The equipment needing frequent internal cleaning or replacement of internal parts should be laid out for ease of maintenance.

Elevation to the underside of the pipe bridges and racks over paved areas should be at least 4 m.

8.2.3 Layout of equipment

Thought should be given to the location of equipment requiring frequent attendance by operating personnel and the relative position the control room to obtain the shortest and most direct routes for operators when on route operation. However, the control room should be in a safe area. Some important considerations involved in locating a few key equipment items are listed below:

• Mixing vessels can be laid out in a straight line, in pairs or staggered.

• In evaporators using barometric leg type condensers, barometric leg should be at least 10 mm from the vessel base. This is usually situated on the ground floor. For multiple effect evaporators, place the individual effects as close as possible to minimize vapor lines. Vapor liquid separator is accommodated without increasing the distance between effects. The layout requirements for crystallizers are similar to those for evaporators.

• Furnaces should be located at least 15 m away from other equipment. Ample room need to be provided at the firing front for the operation of the burner and burner control panel.

• Where there are a large number of heat exchangers, they are often put together in one or more groups. Location should provide a layout, which is convenient to operate and maintain. Horizontal clearance of at least 1.5 m should be left between exchangers or exchangers and piping. Floating head heat exchangers require an installation length of at least 2.5 times the tube length. Air cooled exchangers are located adjacent to the plant section they serve.

• Pumps in general should be located close to the equipment from which they take suction. Changes in direction of the suction line should be at least

• 0.6 m from the pump. As far as possible, clearances and piping should provide free access to one side of the motor and pump. Clearances between pumps or pumps and piping should be at least 1.2 m for small pumps (18 kW) and 1.5 m to 2 m for large pumps. Pumps handling hot liquid (60 °C) should be at least 7.5 m from pumps handling volatile liquids.

8.2.4 Space  determination

In the layout planning process the space is allotted to different activities.

The theoretical minimum space, a plant can occupy, is the total volume of its various components. Various constraints prevent the attainment of this minimum. Such constraints include allowing adequate clearances for access during operation and maintenance and to allow safe operation. While determining the space consideration should be given to the following.

• Operating equipment

• Storage

• Service facilities

• Operators/workers

Allowance must be made for space between adjacent equipment/machines for movement of the worker, work-in-process, maintenance personnel etc.