Milk Plant Essay Example for Free

Milk Plant Essay Activities related to various milk reception take place in this milk reception dock. Obviously, this section should have adequate space for unloading of cans, sampling, grading, weighing, testing and storage of milk and cleaning of cans. Generally this RMRD is provided with interconnected chain conveyors to transfer the cans from the unloading point to the weigh balance and from the outlet of the can washer to the loading point. Other equipment that find a place in this RMRD include weigh balance, dump tank, can washer etc. Milk Processing Section It is located next to the RMRD section. This section shall be spacious enough to accommodate milk chiller, pasteurizer (usually HTST in large dairies), homogenizer, cream separator, milk storage tanks, Cleaning In Place tanks (CIP tanks) and reconstitution unit. Raw milk tanks are generally located at an elevated level Milk Filling Section Sachet filing machines are installed in this section. Standardized, pasteurized milk is stored in tanks located at higher level than the ground to facilitate gravity feeding. The filled up pouches are transferred by conveyor belt and stored in crates and in turn the crates are moved to the chilling chamber which is located next to the milk filling section. Immediately next to the milk filling section is the crate washer room which supplies cleaned crates to the filling section continuously. Milk Production Section This section is located adjacent to the milk processing section. The surplus fat obtained during the cream separation operation is processed as cream and this section includes cream storage tanks, butter churn, butter melting vat, ghee boilers, ghee storage tanks and ghee filling and packaging units. Deep freezer capable of bringing down the temperatures up to -30 °C is kept in this section for preserving the dairy products. Byproduct section This room is located next to the milk product section. The equipment and the utensils that find a place in this section include casein drying unit, casein vat, sour cream separator, butter churn for sour cream and facilities to handle curdled milk. Parlour Products Section In this section, equipment for the value added products like ice cream, peda, masala butter milk, shrikhand etc are provided. Milk Drying Section. In a bigger dairy, milk condensing and drying units are usually installed. This include milk condensing plant, condensed milk tanks, homogenizer, spray or drum drying equipment, nitrogen packaging chamber, and tins and carton packaging units. Quality Control Laboratory The quality control section is generally located near or at least easily accessible to the raw milk receiving dock. It has facilities to test the fluid incoming milk, milk products testing, packaging materials testing, bacteriological and mycological analysis and AGMARK grading sections. Naturally, this section accommodates all the equipment required for the quality control tests. Refrigeration and Boiler Sections Though considered auxiliary to the main dairy operations, the refrigeration and boiler sections nevertheless, do play a vital role in the processing of milk and dairy products. They can be housed in the main dairy building itself or located in a separate building adjacent to the main plant. The refrigeration section consists of ammonia compressors, receivers, chilled water tanks, etc. Condensers are usually located on the roof of the refrigeration section or outside the building. The boiler section includes the boilers, water softening units, water tanks for soft water storage and coal storage or furnace oil storage section. UTILITY Power used-11kv Transformer-750VA transformer(step down) By using it we step down voltage levels from 33kv to 11kv for distribution to substations where the 11kv is further stepped down to 415v. [pic] Low tension panel is used- Metering Panel Board- These Metering Panel Boards are made of16/2mm/ 2. 5 mm cold rolled, mild steel metal clad, free standing, totally enclosed, cubicle type, fully compartmentalized, outdoor / indoor installations and suitable for operation on 11kV, 3ph, 50Hz. , and AC earthed system. The panel contains the equipments and components complete with bus bar interconnections, control wiring, designation labels, caution notices, EB sealing and pad locking facilities wherever required. [pic] MV PANEL- The Switchboards are designed and developed keeping in mind future expansion of the Industry. All the enclosures are fabricated out of 16/14 SWG CRCA steel sheets and they are also powder coated [pic] DISTRIBUTION PANEL Distribution Panels or panel board is a type of component of electricity supply system that is used for the division of electrical power feed into subsidiary circuits. It provides a protective fuse or circuit breaker in a common enclosure. There is provision of a main switch, one or more residual [pic] STEAM- PRESSURE OF STEAM-14kg/cm2, 14 bar Types of Boilers There are many different types of boilers in the boiler room today in a variety of heating applications. There are two main categories of boilers among the different types of boilers and those two categories are steam and hot water boilers. Either of those categories can be fueled by oil, gas, or electric (although electric is uncommon for steam boilers). They have different designs and piping configurations as a steam boiler system is designed to turned the water into steam and uses gravity and pressure to deliver the heat and the hot water boiler systems are designed to simply make hot water to be circulated (by a circulator or pump) through a piping system to provide heat. Typically, hot water boilers are more efficient than steam boilers for a few reasons. First, there is less heat loss throughout the hot water piping and the shell of the boiler because the hot water boiler operates at a lower temperature than the steam boiler. This means there is less heat loss throughout the entire boiler and piping system. Secondly, because the hot water boiler operates at a lower temperature, it requires less fuel or energy to convert into heat. What kind of boiler do you have in your boiler room? [pic] Water Tube Boilers Water tube boilers have many different tubes inside of it that have water circulating through them. Hot combustion gases surround these tubes and an exchange of heat is realized from the combustion gases to the tubes and water. The water tube boilers can be built for higher capacities and pressures than the fire tube boilers because the steam and/or hot water is confined in the tubes. Water Tube Boiler sizes range from from 10 million BTU/h boilers all way up to 300 million BTU/h and these boilers are generally found in medium to large commercial/industrial use and can be either steam or hot water boiler in low to high pressure boiler applications. These boilers can be either oil boiler, coal boiler, or gas fired boiler and pass hot flue gases around tubes filled with water. Boiler combustion efficiencies depend on several factors for these boilers including: whether it is steam boiler or hot water boiler, combustion controls, flue dampers, frequency of tune-ups and/or air and/or water pre-heaters (boiler economizers). Fire Tube Boilers Fire tube boilers confine the combustion process and gases in tubes and water circulates around these tubes. Some fire tube boilers have turbulators inside of the tubes to cause turbulence of the flue gases. This increases the heat absorption into the water which makes the boiler more efficient. Fire Tube Boilers range in sizes from . 6 million BTU/h up to 50 million BTU/h boiler these use hot flue gases passing through tubes submerged in water generally found in medium to large boiler commercial/industrial use and can be either steam or hot water boilers in low to medium pressure applications. Again as with the water tube boiler combustion efficiencies depend on several factors as noted above. There are various names applied to different fire tube boilers such as: Scotch Marine, locomotive, firebox, and vertical or horizontal return tube. Condensing Boilers [pic] Condensing Hot Water Boiler Between steam and hot water and water tube and fire tube boilers there exists conventional atmospheric boilers and condensing boilers. The condensing boiler is far more efficient than the conventional atmospheric boiler. A condensing boiler typically has two heat exchangers and absorbs more heat from the flue gases. It actually absorbs so much heat from the gases that moisture in the flue gases condenses and needs a drain to drain off. This condensed liquid is highly corrosive and it is necessary for the manufacturer to build the condensing boiler out of special materials to prevent corrosion to the equipment. Typically, the flue is PVC pipe or stainless steel and is resistant to the corrosive effects of the condensation. Additionally, because so much heat is removed from the flue gases, the products of the combustion process need help to be safely vented. Usually a fan is used to either push or pull these gases out of a vent. Condensing boilers are typically rated at 90 plus efficiency ratings whereas the conventional atmospheric boilers are typically rated at around 80 percent plus. Conventional Atmospheric Boilers Conventional atmospheric boilers do not use a blower motor to remove the combustion byproduct gases. Instead they rely on the combustion gases to have enough heat to cause the gases to rise through the flue and channeled safely outside of the dwelling. If for some reason too much heat is removed from the flue gases condensation can occur inside the flue or chimney. This condensation can have corrosive effects to both the flue and the chimney and cause severe problems. It is important that a qualified HVAC technician inspect the boiler and that they check of the temperature of the flue gases. Using a combustion analyzer, a qualified technician can tune the boiler to make sure that the temperature of the flue gases is set to optimum levels so that the gases will properly vent and that the gases do not have too much heat in them. If the flue gases are too hot then you are losing efficiency up the flue. If the flue gases do not have enough heat in them then you can have condensation issues which cause corrosion. Have your boiler checked and inspected at least annually to maintain optimum efficiency. Electric Boiler One other type not mentioned above is the electric boiler. One could say that an electric hot water heater is an electric boiler although there are electric boilers that can heat water to steam temperatures. Boilers can use many types of fuels (oil, gas, coal, wood, and electric power) to heat water (or other liquids) but the main focus of Boiler Types article was to categorize the mechanical aspects and differences. [pic] Designing a process line In the dairy raw milk passes through several stages of treatment in various types of processing equipment before reaching the consumer in the form of a finished, refined product. Production usually takes place continuously in a closed process, where the main components are connected by a system of pipes. The type of treatment involved and the design of the process depend on the end product. The process described in this chapter is general milk pasteurisation. This process is the basic operation in market milk processing, and also constitutes an important pretreatment stage in a chain of dairy processes such as cheesemaking and cultured milk production. The aim is to present some of 190 Dairy Processing Handbook/chapter 7 the considerations which the plant designer has to face when planning a whole milk pasteurisation plant. Process design considerations There are many aspects to be considered when a process line is designed. They can vary and be very complex, which places considerable demands on those responsible for the preliminary planning. Project engineering always involves a compromise between different requirements such as: †¢ Product-related – concerning the raw material, its treatment and the quality of the end product. †¢ Process-related – concerning plant capacity, selection of components and their compatibility, degree of process control, availability of heating and cooling media, cleaning of process equipment, etc. †¢ Economic – that the total cost of production to stipulated quality standards is as low as possible. †¢ Legal – legislation stipulating process parameters as well as choice of components and system solutions. Fig. 7. 1 Generalised block chart of the milk pasteurisation process. The process illustrated in figure 7. 1 deals with heat treatment – pasteurisation – of whole milk, e. g. market milk for sale to consumers. Some legal requirements In most countries where milk is processed into various products, certain requirements are laid down by law to protect consumers against infection by pathogenic micro-organisms. The wording and recommendations may vary, but the combination below covers the most commonly stated requirements: †¢ Heat treatment The milk must be heat treated in such a way that all pathogenic microorganisms are killed. A minimum temperature/holding time of 72 °C for 15 seconds Holding Tube Raw milk storage Heat Treatment intermediate storage Clarification process illustrated in figure 7. 1 deals with heat treatment – pasteurisation – of whole milk, e. g. market milk for sale to consumers Some legal requirements In most countries where milk is processed into various products, certain requirements are laid down by law to protect consumers against infection by pathogenic micro-organisms. The wording and recommendations may vary, but the combination below covers the most commonly stated requirements: †¢ Heat treatment The milk must be heat treated in such a way that all pathogenic microorganisms are killed. A minimum temperature/holding time of 72 °C for 15 seconds must be achieved. †¢ Recording The heating temperature must be automatically recorded and the transcript saved for a prescribed period of time. †¢ Clarification prior to heat treatment As milk often contains solid matter such as dirt particles, leucocytes (white blood corpuscles) and somatic cells (of udder tissue), it must be clarified. Since pasteurisation is less likely to be effective if bacteria are ensconced in lumps and particles in the milk, clarification must take place upstream of heating. Milk can be clarified in a filter or, more effectively, in a centrifugal clarifier. †¢ Preventing reinfection Heat exchangers are calculated so that a higher pressure should be maintained in the pasteurised milk flow compared to the unpasteurised milk and service media. If a leakage should occur in the heat exchanger, pasteurised milk must flow into the unpasteurised milk or cooling medium, and not in the opposite direction. In order to safeguard that a booster pump to create a pressure differential is often required and in certain countries it is mandatory. In the event of temperature drop in the pasteurised product due to a temporary shortage of heating medium, the plant must be provided with a flow diversion valve to divert the insufficiently heated milk back to the balance tank. Equipment required The following equipment is required for a remote controlled process: †¢ Silo tanks for storing the raw milk. †¢ Plate heat exchanger for heating and cooling, a holding tube and a hot water unit. †¢ Centrifugal clarifier (as only whole milk is to be treated, a centrifugal separator is not needed in this example). †¢ Intermediate storage tank for temporary storage of processed milk. †¢ Pipes and fittings for connecting main components and pneumatically operated vaves for controlling and distributing the product flow and cleaning fluids. †¢ Pumps for transportation of milk through the entire milk treatment plant. †¢ Control equipment for control of capacity, pasteurisation temperature and valve positions. †¢ Various service systems: – water supply – steam production. – refrigeration for coolant – compressed air for pneumatically operated units – electric power – drain and waste water. Most of the various service systems are described in chapter 6. 11. Service media requirements are calculated after the plant design is agreed upon. Thus the temperature programme for pasteurisation must be known, as well as the specifications for all other areas where heating and cooling are needed (cold storage, cleaning systems, etc. ), before the number and power of electrically operated machines, number of pneumatically operated units, working hours of the plant, etc.can be determined. Such calculations are not presented in this book. Choice of equipment Silo tanks The number and size of silo tanks are determined by the raw milk delivery schedules and volume of each delivery. In order to operate the plant continuously without stoppages due to lack of raw material, a 7-hour supply of [pic] raw milk must be available. Preferably the milk should have been stored for at least 1 – 2 hours before being processed, as natural degassing of the milk takes place during Legal requirements for: †¢ Heat treatment. †¢ Recording †¢ Clarification prior to heat treatment †¢ Preventing reinfection According to regulations set by the European Communities the heat treatment equipment must be approved or authorised by the competent authority and at least fitted with †¢ automatic temperature control †¢ recording thermometer †¢ automatic safety device preventing insufficient heating †¢ adequate safety system preventing the mixture of pasteurised or sterilised milk with incompletely heated milk and †¢ automatic recording device for the safety system referred to in the preceding intent. 192 Dairy Processing Handbook/chapter 7 that period of time. Short periods of agitation are acceptable, but agitation is not really needed until about 5 – 10 minutes before start of emptying, to equalise the overall quality. This avoids interference with the natural degassing process. Plate heat exchanger The main aim of pasteurising milk is to destroy pathogenic micro-organisms. To achieve this, the milk is normally heated to not less than 72 °C for at least 15 seconds and then cooled rapidly. These parameters are stipulated by law in many countries. [pic] When the relevant parameters are known, the platage (dimensioning) of the plate heat exchanger can be calculated. In the present example, the parameters are: †¢ Plant capacity 20 000 l/h †¢ Temperature programme 4 °C – 72 °C – 4 °C †¢ Regenerative effect 94% †¢ Temperature of the heating medium 74 – 75 °C †¢ Temperature of the coolant +2 °C The demand for service media (steam, water and ice-water) is also calculated, as this substantially influences the choice of valves for steam regulation and ice-water feed. Connection plates between the sections of the plate heat exchanger are provided with inlets and outlets for product and service media. The inlet and outlet connections can be oriented either vertically or horizontally. The ends of the plate heat exchanger (frame and pressure plate) can likewise be fitted with inlets and outlets. Dimensioning data for the plate heat exchanger are given in chapter 6. 1. Hot water heating systems Hot water or saturated steam at atmospheric pressure can be used as the heating medium in pasteurisers. Hot steam, however, is not used because of the high differential temperature. The most commonly used heating medium is therefore hot water typically about 2 – 3 °C higher than the required temperature of the product. Steam is delivered from the dairy boiler at a pressure of 600 – 700 kPa (6 – 7 bar). This steam is used to heat water, which in turn heats the product to pasteurisation temperature. The water heater in figure 7. 2 is a closed system consisting of a specially designed, compact and simple cassette type of plate heat exchanger (3) equipped with a steam regulating valve (2) and a steam trap (4). The service water is circulated by the centrifugal pump (5) via the heater (3) and the heating section of the pasteuriser. The function of the expansion vessel (7) is to compensate for the increase in the volume of the water that takes place when it is heated. The system also includes pressure and temperature indicators as well as safety and ventilation valves (8). Temperature control A constant pasteurisation temperature is maintained by a temperature controller acting on the steam regulating valve (ref. 2 in figure 7. 2). Any tendency for the product temperature to drop is immediately detected by a sensor in the product line before the holding tube. The sensor then changes the signal to the controller, which opens the steam regulating valve to supply more steam to the water. This increases the temperature of the circulating water and stops the temperature drop in the product. Holding The length and size of the externally located holding tube are calculated according to the known holding time and hourly capacity of the plant and the pipe dimension, typically the same as for the pipes feeding the pasteurisation plant. Dimensioning data for the holding tube are given in chapter 6. 1. Typically the holding tube is covered by a stainless steel hood to preventing people from being burnt when touching and from radiation as well. Pasteurisation control It is essential to be certain that the milk has in fact been properly pasteurised before it leaves the plate heat exchanger. If the temperature drops below 72 °C, the unpasteurised milk must be kept apart from the already pasteurised product. To accomplish this, a temperature transmitter and flow diversion valve are fitted in the pipe downstream of the holding tube. The valve returns unpasteurised milk to the balance tank if the temperature transmitter detects that the milk passing it has not been sufficently heated. Pasteuriser cooling system As already noted, the product is cooled mainly by regenerative heat exchange. The maximum practical efficiency of regeneration is about 94 – 95%, which means that the lowest temperature obtained by regenerative cooling is about 8 – 9 °C. Chilling the milk to 4 °C for storage therefore requires a cooling medium with a temperature of about 2 °C. Ice water can only be used if the final temperature is above 3 – 4 °C. For lower temperatures it is necessary to use brine or alcohol solutions to avoid the risk of freezing cooling media. The coolant is circulated from the dairy refrigeration plant to the point of use as shown in figure 7. 4. The flow of coolant to the pasteuriser cooling section is controlled to maintain a constant product outlet temperature. This is done by a regulating circuit consisting of a temperature transmitter in the outgoing product line, a temperature controller in the control panel and a regulating valve in the coolant supply line. The position of the regulating valve is altered by the controller in response to signals from the transmitter. The signal from the transmitter is directly proportional to the temperature of the product leaving the pasteuriser. This signal is often connected to a temperature recorder in the control panel and recorded on a graph, together with the pasteurisation temperature and the position of the flow diversion valve. Booster pump to prevent reinfection Care must be taken to avoid any risk of contamination of the pasteurised product by unpasteurised product or cooling medium. If any leakage should occur in the pasteuriser, it must be in the direction from pasteurised product to unpasteurised product or cooling medium. This means that the pasteurised product must be under higher pressure[pic] than the medium on the other side of the heat exchanger plates. A booster pump, ref. 2 in figure 7. 3, is therefore installed in the product line, either after the holding section or before the heating section. The latter position minimises the operating temperature of the pump and prolongs its life. The pump increases the pressure and maintains a positive differential pressure on the pasteurised product side, throughout the regenerative and cooling sections of the pasteuriser. Installation of a booster pump is specified in the legal requirements for pasteurisation in some coun The complete pasteuriser A modern milk pasteuriser, complete with equipment for operation, supervision and control of the process, is assembled of matching components into a sophisticated process unit. Balance tank The float-controlled inlet valve regulates the flow of milk and maintains a constant level in the balance tank. If the supply of milk is interrupted, the level will begin to drop. As the pasteuriser must be full at all times during operation to prevent the product from burning on to the plates, the balance tank is often fitted with a low-level electrode which transmits a signal as soon as the level reaches the minimum point. This signal actuates the flow diversion valve, which returns the product to the balance tank. The milk is replaced by water and the pasteuriser shuts down when circulation has continued for a certain time. Feed pump The feed pump supplies the pasteuriser with milk from the balance tank, which provides a constant head. Tries . [pic] Flow controller The flow controller maintains the flow through the pasteuriser at the correct value. This guarantees stable temperature control and a constant length of the holding time for the required pasteurisation effect. Often the flow controller is located after the first regenerative section. Regenerative preheating The cold untreated milk is pumped through the first section in the pasteuriser, the preheating section. Here it is regeneratively heated with pasteurised milk, which is cooled at the same time. If the milk is to be treated at a temperature between the inlet and outlet temperatures of the regenerative section, for example clarification at 55 °C, the regenerative section is divided into two sections. The first section is dimensioned so that the milk leaves at the required temperature of 55 °C. After being clarified the milk returns to the pasteuriser, which completes the regenerative preheating in the second section. Pasteurisation Final heating to pasteurisation temperature with hot water, normally of a temperature 2 – 3 °C higher than the pasteurisation temperature (? t = 2 – 3 °C), takes place in the heating section. The hot milk continues to an external tubular holding cell. After the hold, the temperature of the milk is checked by a sensor in the line. It transmits a continuous signal to the temperature controller in the control panel. The same signal is also transmitted to a recording instrument which records the pasteurisation temperature. Flow diversion A sensor after the holding cell transmits a signal to the temperature monitor. As soon as this signal falls below a preset value, corresponding to a specified minimum temperature, the monitor switches the flow diversion valve to diversion flow. In many plants the position of the flow diversion valve is recorded together with the pasteurisation temperature. For the location of the flow diversion valve, various solutions are available to satisfy local regulations and recommendations. Below are three alternatives which are commonly utilised: 1 The flow diversion valve is situated just after the holding cell. Where a booster pump is installed, the valve is located before the pump. If the temperature drops under preset level the valve diverts the flow to the balance tank and the pump stops. The flow in the regenerative and cooling sections thus comes to a standstill (even when no booster pump is integrated). After a short while, without temperature increase, the heat exchanger is emptied, cleaned and sanitised. When satisfactory heating is possible the plant is restarted. 2 The flow diversion valve is located after the cooling section of the plant. Following a drop of temperature the flow is diverted to the balance tank and the plant is emptied of product, cleaned and sanitised. The plant is then ready for restart when the temperature conditions are acceptable again. 3 The flow diversion valve is located between the holding cell and the boster pump. If the temperature drops the valve diverts the flow. The booster pump is not stopped, but other valves around the heat exchanger will automatically be positioned so that the milk in the regenerative and cooling sections will be circulated to maintain the right pressure in the plant. This also preserves a proper temperature balance. When the heating conditions are acceptable the process can be resumed without intermediate cleaning. Cooling After the holding section the milk is returned to the regenerative section(s) for cooling. Here the pasteurised milk gives up its heat to the cold incoming milk. The outgoing pasteurised milk is then chilled with cold water, icewater, a glycol solution or some other refrigerant, depending on the required temperature. The temperature of the chilled milk is normally recorded together with the pasteurisation temperature and the position of the flow diversion valve. The graph consequently shows three curves. Centrifugal clarifier As the milk in the present example is not going to be separated into skimmilk and cream, a centrifugal clarifier is shown in figure 7. 6.