Module 4. Design aspects of dairy plant

Lesson 21

21.1 Introduction

A plant will be efficient only if equipment installation is in proper order. Proper order means laying of equipment according to flow pattern of manufacturing process. The equipment must be laid as per sequence of the operations, i.e., ‘what comes next’. Horse has to be put before the cart and not a cart before the horse. For instance, milk after its reception at Milk Reception Dock, has to be weighed, dumped into dump tank, chilled through surface cooler or plat chiller before it is stored into storage tank for further processing. Here a chiller will have to be placed in between dump tank or milk receiving vat and storage tank. Milk route has to be made ass short as possible. Unnecessary travel of men and material should be avoided as it amounts to waste of time. Failure to provide adequate working space may hamper cleaning operations or may cause one operator to obstruct to another, thus causing delay. The positioning of a milk cock or other control just out of normal reach may involve as extra journey or additional effort in getting the means to perform the operation involved. Placing a conveyor or milk pipe across the route which an operator will have to take in the normal course of his duties may cause obvious difficulties and may lead to accidents which, apart from other ill effects, reduce operating efficiency. It is often seen that wrong planning and faulty installation of equipment leads to inefficiency, delays and loss of money as plant becomes uneconomical. Therefore, proper arrangement of equipment is essential for any successful plant.

21.2 Secondary Equipment

Secondary equipment are those equipment which are not directly related to milk such as boilers, compressors, condensers and workshop equipment. These equipment should be in a separate room from the main part of the dairy plant. Equipment, such as brine pumps, chilled water pumps and hot-water circulating units and controls should be located in a separate room or beneath the floor away from processing section.

21.3 Bulk Milk Receiving

A minimum clearance of 5 ft (152 cm) above the highest milk tanker should be allowed for cleaning spray head and balancer. An 8 ft (244 cm) working space should be provided behind each tanker for ease in handling the hose and making connections. The floor at rear of the truck should slope ¾” per ft (1.9cm/30cm) for fast drainage.

21.4 Arrangement of Processing Equipment

The main idea for proper arranging the equipment is to achieve maximum efficiency and economy in respect of installation of the equipment and to provide facilities to staff looking after the equipment for smooth running of the plant. For planning a layout of the equipment, use of layout planning table and model planning is highly recommended. Consideration must be given to the cleaning-in-place system (C.I.P.) when placing the equipment. Storage tanks should be in a battery such as in a row, so that, a common supply and cleaning solution return line can be in a buttery such as in a row, so that, a common supply and cleaning solution return line can be used for all tanks. The same idea holds true for the arrangement of pasteurizing vats or similar pieces of equipment. Regular order of the equipment installation is essential and must be in accordance with flow pattern of the product.

A pasteurizer would probably comprise the heat exchanger, hot water set, milk pump, float tank and possibly an instrument panel together with the inter connecting milk piping.

A bottling line would consist of a bottle washer, filler, capper, and associated conveyors. These equipment should be installed in regular order without any obstruction in the way.

21.5 Milk Piping

The layout of interconnecting milk piping system should be decided keeping in view the method of cleaning. There are two methods which are commonly adopted for cleaning milk piping. These are: (1) manual cleaning method and (2) cleaning-in-place (C.I.P.) method.

If manual cleaning method is adopted, it must be clear that the pipes have to be dismantled frequently for cleaning operations and for this purpose, it is essential that approach to pipe lines is made very easy, i.e., piping system is easily accessible. For this piping supports from ground (floor) is preferred for supporting overhead pipe lines which are 7 to 8 ft above the ground level. Piping supports should be placed at a distance of about 3 meters or about 10 ft. All pipes carrying milk are of stainless steel as they are easy to clean. Sanitary piping is recommended for dairy industry.

For cleaning-in-place method, approach to pipe line is less important as piping will be dismantled relatively infrequently. Layout of piping in C.I.P. system has to be planned carefully because the purpose is not only conveying or carrying mi8lk but also cleaning. Contamination has to be avoided in all cases. In large installations, it will be necessary to arrange for part of the pipe system to be cleaned while another part is conveying milk, and precautions and safeguards must be incorporated to prevent accidental contamination of milk by cleaning solutions or detergents. A milk piping must be so arranged to minimize loss of product at the end of process run to ensure that all cleaning solutions are removed from plant before use. For C.I.P. cleaning of pipe lines, milk piping may be supported from ceiling. In this metal suspension rods are fixed to ceiling. This gives a clear floor area with no obstruction and operations are carried out smoothly.

21.6 Can Washing

Conditions and environments under which milk and milk products are processed are of great importance to customers. Pollution free environment and cleanliness become the prime factor for dairy industry. Cans in which milk is brought are often washed and cleaned well at dairy. Installation position and arrangement of can washing machine in relation to other respective equipment must be done in such a way so as to avoid contamination. The can washer must be installed in milk receiving room or at Milk Reception Dock covered from sides. It has to be placed adjacent to weigh tank (milk dump tank) in between dump tank and can washer, there will be drip saver so that any droplet left again goes back to weight tank. Milk may be transported upto tipping point on can trolleys or by means of conveyors. A stand by washing trough with cold and hot water facilities can be helpful in case of emergency. It will be clearly noticed that ‘can cycle’ ends at milk reception / milk receiving room only as after cans are washed, these are loaded on the same vehicle in most of cases and returned back to milk producers for next day bringing milk. Some space equal to one hour load capacity has to be kept on floor for washed empty cans as precautionary measure. Ultimately these have to be picked up within an hours time. A minimum of 3 ft. distance is desirable between drump tank and can washer may be rotary or straightway can washer.

21.7 Pasteurizer, Homogenizer and Ice-Cream Freezer

As mentioned earlier under arrangement of processing equipment, pasteurizer and other relative equipment along with it have to be installed in order. But there are some other accessory equipment which are integrated into HTST and UHT pasteurizers. These are clarifiers, separators and homogenizers. Clarifiers and separators when installed so as to operate on the heated product must be connected in such a way that they will not reduce the holding time below the legal minimum.

As all fluid milk and all ice-cream mix are homogenized, homogenizers are integrated into continuous pasteurizing systems. Homogenizing temperature must be at least 120 oF. The homogenizer must be located either between the regenerator and heater section or after the heater. Homogenizers work better when the product is delivered to the suction manifold under positive pressure than when they must draw the product into the suction manifold. The timing pump and down stream resistances supply the necessary pressure in most installations, but when there is a lack of pressure on the suction manifold, a centrifugal pump immediately upstream is recommended. It should be electrically connected, so that it can run only when homogenizer motor is running.

Ice-cream freezers and hardening room: Hardening cabinets (for small units) must be placed close to homogenizer. If a plant is incorporating a separate section for ice-cream making, then all relative equipment for ice-crfeam manufacture have to be installed in regular order sequence-wise.

21.8 Consideration of Cleaning-in-Place System

Cleaning in place C.I.P. means in place cleaning of equipment, i.e., cleaning solutions are brought to equipment and cleaned there only instead of equipment being dismantled and taken to separate place for cleaning. For proper performance of any C.I.P. system, all pipe lines must be properly fitted, properly pitched and rigidly supported. Special attention must be given to the supporting arrangement since proper support alone can assure maintenance of proper fit and pitch. Gaskets and joints which are protected from stress will be long lived and trouble-free. Conversely, joints subjected to strain because of vibration, lack of support or poor fit will invariably cut, deform and eventually fail completely. Ingenuity is essential in solving mounting problems at hand when installing C.I.P. system.

General recommendations regarding installation of C/A systems and C/A cleaned equipment are given below:

(i) Tank trucks which are to be spray cleaned should be pitched at ¼ inch per foot from front to rear to provide for efficient high speed unloading and cleaning operations.

(ii) Storage tanks that are to be spray cleaned should be pitched at ¼ inch per ft from rear to front to provide rapid drainage and continued positive recirculation of cleaning solution.

(iii) Where tanks are associated fill-discharge header systems are to be mechanically cleaned, these tanks should be installed with the outlets 18 to 24 inches(45cm to 60 cm) above the floor, or higher, if necessary to accommodate the required number of lines. This height provides good return solution flow from tank washing operations and places all valves at a height convenient to the operator for product-flow control and cleaning.

(iv) All product lines should pitch continuously to pumps being supplied by these lines.

(v) All product transfer lines should pitch from a point above the transfer pump involved continuously if possible toward the constant level tank, storage tank, or filler bowl being supplied.

(vi) All C.I.P. cleaned product lines should pitch continuously towards one or more drain ports.

(vii) Tank cleaning return lines should pitch continuously from the tanker outlet valve to the cleaning return pump involved.

(viii) All connections should fit precisely, so that nipples and elbows can be easily installed and removed for making product piping and C.I.P. connections.

21.9 Arrangement of Boiler House and Refrigeration Machinery

The boiler house is constructed on ground floor with approach from large bay for the removal and replacement of plant. The boiler accessories room is attached to it. Its ideal location is near most steam consuming areas especially milk drying and condensing. It should be on one side of the building away from prevailing winds, if solid fuel is used for obvious reasons of dust and ash. Fuel storage must be adjacent to the boiler house and must have good approach for transport. In any case boiler section must be away from main processing sections.

Refrigeration machinery should be planned so as to locate it centrally. The compressor room and chilled water tank may be placed in a basement and this may have some advantage in warm climates. A ready emergency exit must be provided in the room. It is preferable to have refrigeration room on the ground floor as it will be easy for installation and replacement of equipment. In large plant compressor room may be near the boiler in a separate building

21.10 Conveyors

Whenever question of material handling comes, thought must be given to available material handling devices, such as, cart, trolleys, fork lift truck, conveyors, etc. All these devices save labour and time. Not only efficiency is achieved but delays are also curtailed. Out of all these for constant and organized movement of the product from one point to another conveyers are the best. Other devices are good for small operations. Conveyors should be properly liad out, timed and provided with convenient shut off switches. They should be so located that they do not block passages. Automatic controls for speed control and stopping in the event of a pile-up are desirable. The length of conveyor between two pieces of equipment is important and serves as a storage to aid in synchronizing the speed of the two machines. This storage function gives the operator a brief period in which to correct minor difficulties with a machine without stopping the entire line. Conveyor sections can be mounted on wheels which can be rolled into position to extend the fixed conveyors to load trucks, if necessary.

21.10.1 Types of conveyors

Conveyors move cases and cans faster and more efficiently than men and this increases the proportion of time workers who can spend more time on actual production work. The most common types of conveyors used in dairy industry are:

1. Chain conveyor 2. Belt conveyor

3. Gravity conveyor (roller conveyor) 4. Wheel conveyor

Chain conveyors are the type most widely used in the dairy plant to convey crates, cans and other packages. Chain conveyors are of three types: (1)above floor type, (2)infloor type, and (3)on floor type. Regardless of the type, every chain conveyor system consists of 4 basic parts, namely (1) power uni, (2) conveyor frame, (iii) chain, and (iv) take up unit.

All complete chain conveyor systems may consist of one or more power units depending upon the size of the plant and the complexity of the package handling flow in plant.

Above floor chain conveyors have an open type steel welded or bolted frame. The chain is pulled along in the hardened steel chain tracks mounted in this frame – usually foot above the floor. The return chains run in channels mounted in the frame below the carrying chains. The standard chain height for an above-floor conveyor in most plants is between 18 and 22 inches. This is because the top of the case is generally 30 to 36 inches off the floor, which is the most convenient working height for most washer and filler operators. This type of conveyor is used to convey single cases and cans. The conveyor frame has side rails that extend up above the top of the chain to keep the case and can on the conveyor.

The in-floor type conveyor is a double chain conveyor imbedded in the floor. The infloor type conveyors cost same as above floor type conveyors except that installation cost is slightly higher because of the necessity of supplying in floor pits for drives and take up units. Also cost of additional work required to imbed the conveyor in the floor flush with floor level. The frame consists of a steel plate 1/8 to 3/16 inch thick, formed with channels for the carrying and return chains, so that the overall width of frame is about 16 inches. The conveyor frame is embedded in the floor. The two carrying chains are usually ½ inch above the floor level. The return chain travel is between and below the carrying chains.

In-floor conveyors must be planned in the initial stages, because a floor channel has to be provided to accommodate them and to house driving motor. The pits for driving motors are made large enough for cleaning and maintenance and are covered by removable steel plates or grids. With infloor conveyors, the entire area where the conveyor is located is free from those conveyors which must be climbed over to get around the plant.

Belt conveyors

Belt conveyors are used in dairy plants for carrying cases between floors in multistory plants. These are also used in the dry storage warehouses for unloading warehouse items from delivery trucks. Belt conveyors are not suited for handling milk cans.

Gravity-roller conveyors and wheel conveyors

Gravity-roller conveyors and wheel conveyors are used today to a limited extent. These conveyors find their use in warehouse and for short sections or lift sections at the end of power conveyor systems. Wheel conveyors are ideal for warehouse operations because they are light in weight, portable and are easily moved around in the ware house.

Bottle conveyors

Bottle conveyors are of two types, namely (1) Flat link, and (2) the lateral curve. Both have a smooth level surface and can be used for either glass or paper bottles. It will be noted that bottles require slat conveyors to give the necessary area of flat surface for stability. Bottle conveyor is a type of chain conveyor using chains which may have from a 1 to a 4 inch pitch. The drive unit is usually of the gear-motor variety located at one end of the conveyor and pulling the chain through the system to an idler sprocket at the other end. The chain runs on a frame between the rails. Conveyors are installed as per requirement of a particular section.

21.11 Typical Equipment Layouts

Typical equipment layouts are shown in the Fig. 21.1, Fig. 21.2, Fig. 21.3, and Fig. 21.1 (1), Fig. 21.4 (2), Fig. 21.4 (3), Fig. 21.4 (4), Fig. 21.4 (5), Fig. 21.4 (6), Fig. 21.4 (7), Fig. 21.4 (8), Fig. 21.4 (9), shows symbols for different equipments.

Last modified: Wednesday, 26 September 2012, 10:17 AM