Lesson 5. Food plant size and utilities

5.1 Plant size

Plant size / capacity for any food-processing unit refer to the planned rate of production of the identified product(s). It can be expressed in terms of either volume or weight or number produced per unit time of the product. The time unit for expressing the plant size could be taken as hour or a shift or a day or a year. It is always useful to take a decision about the size/capacity in the beginning of the plant design.

Knowledge of the plant size may help in:

  • assessing the type and size of the plant and machinery needed

  • assessing the size and caliber of the work force needed

  • determining the requirements of total land area and covered space for the plant

  • deciding the type of layout

  • assessing the other physical facilities needed

  • determining the type of sales efforts and distribution system

  • financial or economic viability calculations

The size/capacity of the plant will depend on a number of factors such as:

  • raw material availability

  • market demand

  • degree and nature of the market competition

  • economic considerations i.e. acceptable return on investment / profitability

The interaction of each of the above factor with plant size can be assessed on the basis of information collected as part of the market study. Therefore, a comprehensive market study is a must.

5.1.1 Raw material availability

There may be adequate or unlimited demand for the product in the market with little or no competition, but the entrepreneur may not get adequate supplies of the raw material to produce the product in quantities one wishes. This would limit the size.

5.1.2 Market  demand

Market demand for any product is the total volume that will be bought by a defined customer group in defined geographical area in a defined time period and in a defined environment. It is possible that the raw material is available in abundance. One can get as much raw material as one wish. But one can not sell all that one can produce. The demand for the product is limited. In this case, it is the market demand, which will determine the plant size.

5.1.3 Degree and nature of the market competition

There is no restriction on raw material availability. It is available in abundance. Also, there is enough demand for the product in the market. However, there exist a large number of manufacturers / processors for the product who are expected to provide stiff competition. In this case, the plant size may be restricted to a limit governed by the share of the market, which the entrepreneur may capture. Depending on the product, a 10 - 15% market share is considered to be adequate. The competition may involve price or quality or timely delivery or a combination of such features. To study the competition, the entrepreneur needs to have a list of major competitors, details of their product range, product features, output, market share and pricing.

5.1.4 Economic Considerations

Many times plant size is determined by the financial resources available with the entrepreneur as also by the degree of risk the entrepreneur is prepared to take. Sometimes it is also advisable to find the popular plant size of existing enterprises engaged in manufacturing/processing the product of choice.

In cases where the availability of raw material, market demand and the financial resources are not a problem, the entrepreneur may look for the size which will ensure him / her a minimum acceptable return/profit. This size is called the minimum economically viable plant size. However, when situation permits a plant size larger than the minimum economically viable size, a size, which will maximize profits, is selected.

The minimum acceptable return/profit viewed in two ways. In one case larger share of the capital investment may consist of the equity (entrepreneur's own capital) while in another case it may consist of the borrowed capital. In case of the former, the return/profit must be greater than the amount of interest earned if the entire capital of the entrepreneur was invested as fixed deposit in a scheduled bank. In case of the later, the return/profit must be greater than the interest paid on the borrowed capital.

While deciding the plant size/capacity one should also remember the following:

  • Specify the number of days for which the proposed plant will work in a year. In general, it is customary to presume 300 working days. However, if the enterprise is to handle the seasonal product, it may work for less than 300 days.

  • One shift consists of 8 hours. One shift working is the most popular pattern among small enterprises. Two and three shift working is largely limited to continuous enterprises and the medium and large-scale enterprises.

5.2 Food plant utilities

The principal plant utilities in a food plant are process water, process steam, electric power for motors and lighting, and fuel.

5.2.1 Process Water

Process water is required for washing the raw materials and for various cooling operations. In fruit and vegetable processing plants, water may be used for transportation (fluming) of the raw materials from receiving to processing areas. Water used in steam boilers may require ion exchange treatment to reduce its hardness. Total water requirement in fruit and vegetable processing may range from 5 to 15 m3 / ton of raw material.

5.2.2 Steam

Steam boilers are needed in most food processing plants to provide process steam, used mainly in various operations, such as heating of process vessels, evaporators and dryers, sterilization, blanching, and peeling. A medium size food plant (80 tons / day raw material) may require a boiler producing about 10 tons/h of steam at 18 bar pressure.

Two principal types of steam boilers are used in the food processing industry, i.e. the fire-tube and the water-tube boilers. The fire tube boilers operate at relatively lower pressure (1–24 bar) and produce cleaner steam. The water- tube units operate at higher pressures (100–140 bar) and they are suited for co- generation, i.e. electrical power and exhaust steam of lower pressure for process heating. Co-generation is economical in large food plants, requiring large amounts of low-pressure steam, e.g., beet sugar plants.

A standby steam boiler of proper capacity may be necessary to provide process steam during any boiler failure or breakdown.

Steam boilers are rated in Btu/h, kW or boiler HP (1 Btu/h = 0.293 W, 1 boiler HP = 9.8 kW). The heat flux in the boiler heating surface is about 0.75 kW/ m2. The boiler efficiency is about 85% with most of the thermal losses in the dry gases and the moisture. Steam generation is about 1.4 t/h per MW.

In order to maintain the concentration of accumulated dissolved solids in steam boilers below 3500 ppm, periodic discharge of hot water (blow down) is practiced.

Fuel is used in food plants mostly for generating process steam and process drying. Natural gas and liquefied propane (LPG) are preferred fuels in food processing, because their combustion gases are not objectionable in direct contact with food products. Fuel oil and coal can be used for indirect heating, i.e. through heat exchangers.

Culinary steam of special quality is used when steam is injected in food products. The steam must be free of objectionable chemicals used in boilers, which may be carried into the food being heated. Culinary steam is usually produced from potable water in a secondary system of a heat exchanger heated with high pressure industrial steam.

5.2.3 Electricity

Electrical power in food processing plants is needed for running the motors of the processing, control, and service equipment, for industrial heating, and for illumination. For a medium size food plant processing about 100 tons/day raw materials, the power requirement may of the order of 500 kW. A standby power generator of about 200 k VA is recommended for emergency operation of the main plant, in case of power failure or breakdown.

Single-phase or three-phase alternating current (AC) of 110 V (60 cycles) or 220 V (50 cycles) is used in food processing plants. The electrical motors are either single-phase or three-phase squirrel cage.

Energy-efficient electrical motors should be used in various food processing operations. A measure of the efficiency of electrical power is the power factor (pf), defined as k W/ k VA, this which should be equal or higher than 0.85.

Illuminating (lighting) of industrial food plants should utilize fluorescent lamps, which can save significant amounts of energy.

5.2.4 Plant Effluents

Plant effluents consisting mainly of wastewater, but including solids and gas wastes require special handling and treatments to comply with the local laws and regulations.

Food plants should be designed and operated so that a minimum pollution is caused to the environment. The Environmental Protection Agency (EPA) in the US has issued codes and regulations that ensure the quality of natural water bodies is not damaged by effluent discharges from industrial plants. Similar regulations apply to atmospheric emissions of objectionable gases and dust. Environmental information needed to comply with EPA regulations for wastewater includes testing for pH, temperature, biochemical oxygen demand (BOD), fats oil and grease (FOG), and total suspended solids (TSS).

Large amounts of waste are produced in the processing of fruits and vegetables, as in canning, freezing, and dehydration operations. Smaller waste volumes are produced in dairy plants (with the exception of cheese and milk powder), and in dry-processing (milling) of grain (e.g., wheat flour).

A medium size fruit or vegetable processing plant handling about 100 ton/day of raw materials may discharge about 1000 m3/day of waste water.

Treatment of food waste water may involve one or more of the following operations:

1. Simple screening out of the suspended solids,

2. Gravel filtration,

3. solids settling in sedimentation tanks,

4. biological oxidation (aeration),

5. spray irrigation,

6. discharge into the local public sewer, and

7. discharge into a waterway.

Liquid wastes (waste water) can be disposed to the local waste (sewage) treatment plants, after removing some objectionable components, such as fat, oil, and grease to an acceptable level, e.g., lower than 1000 mg/L. Pollution loads higher than 200 mg/L are common in food plant liquid wastes. It is more economical to pay pollution surcharges to the local sewage plant, whenever possible, than to build an expensive wastewater treatment facility.

Food preservation plants, located away from municipal sewage systems, dispose the process water to large storage ponds (lagoons), where a slow natural bio-oxidation of the organic waste takes place. The treated lagoon wastewater can be discharged to the land adjoining the plants.

Some solid food wastes can be sold at relatively low prices for animal feeds, either unprocessed or dried, e.g., solid citrus or sugar beet wastes. Some solid food wastes can be diverted to the land (grape pomace to vineyard), while some other can be mixed with the soil (composting).

The sanitary sewage of food plants, depending on the number of employees, should be treated in a different system than the process wastewater. It can be discharged to the local sewage system, if available. Otherwise, it is treated in septic tanks constructed near the food plant.

Relatively small amounts of gas wastes (odorous VOC) are generated by some food industries, such as bakeries (ethanol), fishmeal dryers, and edible oil refining plants. Also, odors from coffee and cocoa roasting may require some form of treatment. Treatment of objectionable gas wastes involves gas absorption equipment, such as wet scrubbers.

The design of treatment facilities for industrial wastewater, and solids/gas wastes requires the expertise of environmental engineers who are familiar with the local laws and regulations concerning environmental pollution.

Last modified: Friday, 23 August 2013, 9:19 AM