Dairy Science & Technology · Dairy Engineering & Plant Operations · also Utilities Engineering, Energy Conservation in Dairy Plants
Steam, water, compressed air and electricity in the milk plant, and how to audit and cut energy and water use.
In the exams: ICAR AICE subject 37 Unit 3 (water conservation) and subject 38 Units 4–5; ICAR AIEEA-PG group 18 Unit II (steam generation, compressed air, energy audit)
A dairy plant runs on utilities: steam for heating, refrigeration for cooling, water for cleaning and processing, compressed air for valves and machines, and electricity for everything else. These services account for most of a dairy's energy use, a large part of its operating cost, and much of its environmental footprint. They also carry safety hazards: boilers and pressure vessels can explode, steam scalds, and poor water quality can contaminate products. Managing utilities well is therefore central to cost, safety, product quality and sustainability.
This manual covers boilers, their fittings and efficiency; steam distribution and condensate recovery; water supply, treatment and quality; compressed air systems; electrical supply and power factor; energy audits; heat recovery and cogeneration; renewable energy (solar thermal and biogas); water conservation and reuse; and boiler and pressure-vessel safety rules. Refrigeration is covered in dairy-refrigeration-cold-chain, cleaning and CIP water use in cip-sanitation-hygienic-design, evaporator energy in evaporation-drying-dairy, effluent and cow water in dairy-effluent-environment, and broader water and wastewater principles in the sustainability track's water-wastewater-treatment; this manual concentrates on the utility systems themselves.
ICAR AICE-JRF/SRF Dairy Technology (subject 37, Unit 3) includes water conservation methods, and Dairy Engineering (subject 38, Units 4 and 5) covers thermodynamics, heat transfer and pressure vessels; ICAR AIEEA-PG Food Science group 18 (Unit II) names equipment for steam generation, compressed air, refrigeration, water and wastewater treatment, and energy audit. Values given are representative; national boiler, electrical and environmental regulations and equipment data govern practice.
Steam is the main heat carrier in most dairies: it heats pasteuriser hot-water sets, UHT plants, evaporators, CIP solutions, ghee and khoa kettles, retorts and spray-dryer air heaters. It is produced in boilers. Fire-tube (shell) boilers pass hot combustion gases through tubes surrounded by water in a large shell; they are compact, packaged units with a large water reserve that copes well with fluctuating loads, and they cover the capacities and pressures most dairies need. Water-tube boilers circulate water inside tubes surrounded by hot gases; they suit larger capacities and higher pressures and respond quickly to load changes. Small plants and specific uses may use electric (electrode) boilers, and some processes use thermic fluid heaters, which heat an oil to high temperatures at low pressure. Fuels include natural gas, furnace oil and light diesel oil, coal, and biomass such as rice husk, wood chips and agro-residue briquettes, increasingly favoured for lower fossil carbon emissions; electricity becomes attractive where it is renewable and cheap. The choice depends on fuel availability and price, emission rules, capacity, space and the cost of fuel handling and ash disposal.
Boiler mountings are the devices fitted for safe operation and control, and regulations specify which are mandatory. They include at least two safety valves that release steam if pressure exceeds the set limit; water level indicators (gauge glasses), usually two, to show the water level; a pressure gauge; a steam stop valve to isolate the boiler from the steam main; a feed check valve that admits feed water and prevents back-flow; a blow-down valve to remove sludge and concentrated water from the bottom; a fusible plug in some designs that melts and releases steam into the furnace if the water level falls too low; and low-water alarms and cut-outs. Accessories improve efficiency and operation: feed pumps, feed-water tanks and deaerators (which remove dissolved oxygen and carbon dioxide that cause corrosion), economisers (which heat feed water with flue gas), air preheaters, burners with combustion controls, and, where needed, superheaters (rare in dairies, which use saturated steam). Water level control and burner management systems with flame failure protection are essential safety controls.
Boiler efficiency is measured by the direct method — useful heat in steam divided by heat in fuel: efficiency = steam flow × (enthalpy of steam − enthalpy of feed water) ÷ (fuel flow × gross calorific value). For example, a boiler producing 2,000 kg/h of saturated steam with an enthalpy of 2,770 kJ/kg from feed water at 80 °C (about 335 kJ/kg), burning 140 kg/h of oil with a calorific value of 42,000 kJ/kg, has an efficiency of 2,000 × 2,435 ÷ (140 × 42,000) ≈ 83 per cent. The indirect (heat-loss) method subtracts measured losses from 100 per cent: dry flue gas loss (the largest, rising with flue gas temperature and excess air), loss due to moisture and hydrogen in the fuel, unburnt fuel, radiation and convection from the shell, and blowdown. The evaporation ratio (kilograms of steam per kilogram of fuel) is a simple day-to-day indicator. Efficiency is improved by tuning combustion to the minimum safe excess air (measured by oxygen or carbon dioxide in flue gas), keeping heat-transfer surfaces clean on both water and gas sides, installing economisers, insulating the boiler, recovering condensate, and controlling blowdown. Blowdown is needed to keep dissolved solids in the boiler water below a limit; the blowdown rate as a percentage of feed is feed TDS ÷ (maximum boiler TDS − feed TDS) × 100.
Inside a boiler, water is concentrated as steam leaves, so any dissolved solids in the feed accumulate. Calcium and magnesium salts precipitate as scale on hot surfaces; even a thin layer of scale acts as insulation, raising tube metal temperatures and fuel use, and thick scale can cause tube failure. Dissolved oxygen attacks steel as pitting corrosion, especially in feed lines, economisers and the boiler itself, while carbon dioxide released from bicarbonate in the boiler forms carbonic acid in the condensate and corrodes return lines. Boiler water treatment therefore combines external treatment of the make-up water (softening or reverse osmosis), mechanical deaeration in a heated deaerator or hot well, and internal chemical treatment: oxygen scavengers such as sodium sulphite, phosphate or polymer conditioners that keep residual hardness as a removable sludge, alkalinity control to protect steel, and neutralising or filming amines for condensate lines where these are permitted. Where steam contacts food, only treatment chemicals approved for that use may be present. The boiler operator keeps a log of water tests — hardness, pH, TDS or conductivity, sulphite residual — and adjusts chemical dosing and blowdown accordingly. Continuous (surface) blowdown controlled by conductivity removes concentrated water steadily, while intermittent bottom blowdown removes sludge; heat can be recovered from continuous blowdown through a flash vessel and heat exchanger. Start-up from cold must be gradual to avoid thermal stress, and boilers on standby need wet or dry lay-up to prevent corrosion.
Steam demand is built up from each user: pasteurisers and hot-water sets, UHT plants, evaporators, dryers, CIP heating, ghee boilers and kettles, space and water heating. The peak demand, its timing and the diversity between users determine boiler capacity, usually expressed as kilograms of steam per hour 'from and at 100 °C' — the evaporation the boiler would achieve from feed water at 100 °C to steam at 100 °C — so that boilers of different working conditions can be compared. Plants usually install two or more boilers so that one can be inspected or repaired without stopping production, and so that a boiler is not run at very low load, where efficiency falls and burners cycle on and off. Steam accumulators store steam as hot pressurised water and smooth sharp peaks. Sizing also considers future expansion, fuel storage, chimney height required by emission rules, and the boiler house layout and access needed for inspection.
Dairies usually distribute saturated steam at moderate pressure from the boiler house and reduce it with pressure-reducing valves at the point of use, since saturated steam gives up its latent heat at a constant temperature set by its pressure and lower-pressure steam has more latent heat per kilogram. Steam mains are sized for appropriate velocities, sloped in the direction of flow, drained at low points and before control valves through drip legs and steam traps, and insulated; uninsulated pipes and fittings waste large amounts of energy. Air and non-condensable gases must be vented, because air in steam lowers its temperature at a given pressure and blankets heat-transfer surfaces. Water hammer, caused by condensate slugs carried at high velocity, is prevented by correct drainage and slow warm-up. Steam that contacts food directly — for steam injection, infusion and direct heating — must be culinary steam, produced from potable water or by a clean steam generator, filtered and free from boiler-treatment chemicals that are not permitted in food.
Steam traps let condensate and air out of steam spaces while holding back live steam. Mechanical traps (float-and-thermostatic, inverted bucket) respond to the density difference between steam and condensate; thermostatic traps (balanced pressure, bimetallic) respond to temperature; thermodynamic traps use the dynamics of flash steam over a disc. Each suits different applications: float traps for heat exchangers with modulating loads, thermodynamic traps for mains drainage, thermostatic traps for tracing and air venting. Failed-open traps waste steam continuously, and failed-closed traps waterlog equipment and cut heat transfer; trap surveys using ultrasound or temperature measurement, with repair programmes, are among the most cost-effective energy measures in a dairy.
Condensate leaving a steam user is hot, pure water that contains a significant share of the heat in the original steam and has already been treated. Returning it to the boiler feed tank saves fuel, water, treatment chemicals and blowdown. Condensate from product-contact heat exchangers must be monitored for contamination (for example by conductivity or turbidity) before return, since a leaking exchanger can put milk into the boiler. When high-pressure condensate is released to a lower pressure, part of it re-evaporates as flash steam; the fraction flashed is (sensible heat of condensate at the high pressure − sensible heat at the low pressure) ÷ latent heat at the low pressure. For condensate at about 721 kJ/kg flashed to atmospheric pressure (sensible heat 419 kJ/kg, latent heat 2,257 kJ/kg), about 13 per cent flashes. Flash vessels recover this steam for low-pressure uses such as heating water, rather than venting it as a visible plume of wasted energy.
Dairies use large volumes of water: for cleaning (usually the largest use), for cooling (cooling towers, evaporative condensers, plate coolers), for boiler feed, for product (recombination, standardisation, ingredient water), for domestic purposes and for gardens. Water comes from wells or boreholes, municipal supplies, rivers or reservoirs, and increasingly from recovered water (see the water conservation chapter). Water use per litre of milk processed varies widely with product mix and practice, from around one litre to several litres of water per litre of milk, so plants benchmark themselves against similar plants and their own history.
Water that contacts product or product-contact surfaces must be of potable quality, meeting national drinking-water standards (in India, for example, the Bureau of Indian Standards specification for drinking water; internationally, World Health Organization guidelines) for microbiological, chemical and physical parameters. Beyond safety, process water quality affects operations. Hardness (calcium and magnesium) forms scale in boilers, heat exchangers, evaporators and CIP systems and reduces detergent effectiveness; iron and manganese stain and catalyse oxidation; chlorides corrode stainless steel; silica forms hard scale in boilers; and high total dissolved solids raise boiler blowdown. Boiler feed water has its own limits on hardness, dissolved oxygen, pH and dissolved solids, and cooling-tower water must be controlled for scale, corrosion and microbial growth, including Legionella.
Treatment is matched to source and use. Common steps include screening and sedimentation for surface water; filtration through sand or multimedia filters; activated carbon to remove chlorine, taste and organics; softening by ion exchange, in which calcium and magnesium are exchanged for sodium on a resin regenerated with salt; reverse osmosis to remove most dissolved salts for boiler feed, ingredient water or demineralised needs; demineralisation by ion exchange; and disinfection by chlorination, chloramination, ultraviolet light or ozone. Product water is often chlorinated at a controlled residual and then dechlorinated for some uses. Water storage tanks and distribution pipes are designed and cleaned to prevent contamination and biofilm, and water quality is monitored through a sampling plan as part of the food safety system.
Because water reaches product and product-contact surfaces, it is treated as an ingredient in the food safety system. A water management plan maps every source, treatment step, storage tank and distribution line, identifies the uses of each water quality grade, and sets monitoring: free chlorine residual and pH daily or continuously at key points, microbiological tests (coliforms, Escherichia coli, total viable count) at defined frequencies, and chemical analysis periodically against drinking-water standards. Hoses and outlets are labelled by water grade, cross-connections between potable and non-potable systems are prevented by air gaps or backflow preventers, and storage tanks are covered, cleaned and inspected. Water used for the final rinse in CIP, for cooling product in direct contact, and for ice must be potable; recovered water used for these purposes needs specific validation and, in many countries, regulatory acceptance. Water hardness and alkalinity data also guide detergent choice and CIP programme design, linking utilities with cip-sanitation-hygienic-design.
Compressed air drives pneumatic valves and actuators throughout a modern dairy, operates filling and packaging machines, conveys powders, agitates and aerates (for example ice cream overrun air and fermentation), and is used for cleaning. Air is compressed by rotary screw compressors (most common in medium and large plants) or reciprocating compressors, stored in air receivers that buffer demand and allow condensate to settle, cooled in aftercoolers, dried in refrigerated dryers (to a pressure dew point a few degrees above freezing) or desiccant dryers (to well below freezing, needed where pipes run through cold areas or for sensitive uses), filtered, and distributed through ring mains. Compressed air that contacts food or food-contact surfaces must be oil-free and filtered to defined purity classes for particles, water and oil (the ISO 8573-1 classification is widely used), and oil-free compressors or high-efficiency filtration are used for such duties; sterile filtration is added for aseptic processes.
Compressed air is one of the most expensive forms of energy in a plant: only a small fraction of the electrical energy input ends up as useful work, the rest becoming heat. Leaks are the biggest waste and in many plants account for a large share of compressor output; leak surveys using ultrasonic detectors and prompt repair save energy quickly. Other measures include reducing the generation pressure to the lowest that satisfies users (each bar of reduction saves a noticeable percentage of compressor energy), using variable-speed compressors to match demand, sequencing multiple compressors, avoiding inappropriate uses such as open blowing for cleaning or cooling, shutting off air to idle machines, and recovering compressor heat (most of the input power) to heat water or space. The cost of a leak can be estimated from the compressor power it consumes: a leak equivalent to 5 kW of compressor power running 8,000 hours a year wastes 40,000 kWh.
Compressing atmospheric air concentrates its water vapour, so a compressor delivering air at 7 bar produces litres of condensate every hour in humid weather. This condensate, contaminated with oil in lubricated systems, is removed by aftercooler separators, receiver drains and dryer drains; zero-loss electronic drains discharge only liquid, whereas timed drains that open whether or not water is present waste compressed air. The oily condensate must be separated before discharge to drain, as it counts as an effluent. Filters are changed on differential pressure or schedule, since a blocked filter adds pressure drop and energy use. Air quality at points of use is verified periodically by sampling for particles, water and oil, particularly for air in direct contact with product, packaging or aseptic zones, and the results form part of the food safety records. Pipework of aluminium or stainless steel avoids rust particles that carbon steel mains shed into the air.
Dairies receive electricity from the grid, usually at high voltage for larger plants, stepped down by their own transformers and distributed through switchgear, motor control centres and distribution boards. Standby diesel or gas generators provide backup for critical loads, and in areas with unreliable supply, power quality and backup are major concerns for cold chains and continuous processes. Electricity bills commonly include energy charges (per kilowatt-hour), demand charges based on maximum demand (kVA or kW) in a billing period, power factor penalties or incentives, and time-of-day tariffs. Managing maximum demand by staggering large loads (compressors, homogenisers, spray-dryer fans) and shifting loads to off-peak periods (for example by charging ice banks at night) reduces costs. Electric motors drive pumps, fans, compressors, agitators and conveyors and use most of a dairy's electricity; high-efficiency motors and variable-speed drives are the main savings.
Power factor is the ratio of real power (kW), which does useful work, to apparent power (kVA), which the supply must deliver: power factor = kW ÷ kVA = cos φ. Induction motors and transformers draw reactive power (kVAr) to set up magnetic fields, lowering the power factor. A low power factor means higher current for the same useful power, larger cables and transformers, higher losses, and often tariff penalties. For example, a load of 400 kW at a power factor of 0.8 draws 500 kVA; raising the power factor to 0.95 reduces this to about 421 kVA. Power factor is corrected by installing capacitor banks (often automatically switched) that supply reactive power locally; the capacitor rating needed is kW × (tan φ1 − tan φ2), which for 400 kW from 0.8 to 0.95 is about 400 × (0.750 − 0.329) ≈ 168 kVAr. Harmonics from variable-speed drives and other electronic loads must be considered when installing capacitors, sometimes requiring detuned banks or filters.
For centrifugal pumps and fans, the affinity laws state that flow is proportional to speed, pressure to speed squared and power to speed cubed. Reducing speed to 80 per cent therefore reduces power to about 0.8³ ≈ 51 per cent, which is why variable-speed drives on pumps and fans that previously ran at full speed with throttling valves or dampers save so much energy. High-efficiency motors (for example IE3 and IE4 classes under international standards) cost a little more but repay quickly on motors that run many hours. Correct motor sizing (avoiding oversized motors running at light load), good maintenance, and switching off idle equipment complete the picture. Lighting is a smaller load, but replacing old fittings with LEDs and controls is an easy saving.
An energy audit identifies where and how energy is used in a plant, how efficiently, and what can be done to reduce it. A preliminary (walk-through) audit uses existing data, bills and observation to find obvious savings and to decide where detailed study is needed. A detailed audit measures energy use by area and equipment with portable instruments and submeters — flue gas analysers, power analysers, flow meters, thermal cameras, ultrasonic leak detectors — and establishes energy balances. In India, the Energy Conservation Act (2001) created the Bureau of Energy Efficiency, which certifies energy managers and auditors and requires mandatory audits and energy managers for designated energy-intensive consumers; schemes such as Perform, Achieve and Trade set efficiency targets for some industries. Other countries have similar programmes, and ISO 50001 provides a framework for energy management systems.
A typical detailed audit proceeds as follows: collect data on energy purchases, production and operating hours; map energy flows (often shown as a Sankey diagram); measure the main users — boilers, refrigeration, compressed air, motors and drives, evaporators and dryers, lighting; calculate specific energy consumption (SEC), such as kilowatt-hours of electricity and megajoules of fuel per kilolitre of milk processed or per tonne of product, and compare with benchmarks and with the plant's own history; identify opportunities; estimate savings, costs and simple payback (investment ÷ annual savings — for example an investment of 12 lakh rupees saving 4 lakh rupees a year pays back in 3 years); prioritise; and report. Implementation must be followed by measurement and verification, to confirm that savings occur and persist. Common findings in dairies include steam leaks and failed traps, uninsulated pipes and valves, excess boiler air, lack of condensate return, compressed air leaks and high pressure, oversized and constant-speed pumps and fans, poor refrigeration practice (low evaporating temperatures, dirty condensers), simultaneous heating and cooling, and unmonitored CIP.
Energy use in dairies is roughly split between thermal energy (fuel for steam and hot water) and electricity. Thermal energy dominates in plants that evaporate and dry milk or whey, where evaporators and spray dryers can account for most of the fuel; in liquid milk plants, pasteurisation, CIP and hot water are the main thermal loads, and electricity for refrigeration, pumps and compressed air is a larger share. Typical electrical users in a market milk plant are refrigeration (often the largest), then pumps, homogenisers, compressed air, packaging machines, lighting and ventilation. Specific energy consumption varies widely with product mix, scale, age of plant and climate, so internal trends and like-for-like comparisons are more useful than a single benchmark. Energy is often expressed as primary energy or as carbon dioxide equivalent so that fuel and electricity can be compared, and an energy policy, an energy manager, targets, metering and monthly reviews turn audit findings into lasting savings. Energy monitoring and targeting (M&T) uses regression of energy against production to set expected consumption and flag deviations quickly.
Consider a plant processing 200,000 litres of milk a day that uses 12,000 kWh of electricity and 5,000 kg of furnace oil a day. Its specific electricity consumption is 12,000 ÷ 200 = 60 kWh per kilolitre, and its specific fuel consumption is 25 kg of oil per kilolitre. An audit finds that condensate is not returned, that the boiler runs with high excess air, that the compressed air system runs at 7.5 bar where 6 bar would satisfy all users, and that chilled-water pumps run at full speed against throttled valves. Each finding is quantified: for example, raising condensate return from zero to 60 per cent saves fuel by reducing the heat needed to warm make-up water; tuning the burner to lower excess air reduces flue gas loss; lowering compressor pressure saves several per cent of compressor energy; and variable-speed drives on pumps save energy by the cube law. Each measure gets a cost estimate and payback, and the report ranks them, starting with no-cost and low-cost actions such as repairing leaks, switching off idle equipment and correcting set points.
Dairies heat and cool the same products repeatedly, which makes heat recovery especially valuable. Regeneration in pasteurisers and UHT plants recovers most of the heat from hot product to preheat cold product (see market-milk-processing). Boiler economisers recover heat from flue gas into feed water; as a rule of thumb, lowering flue gas temperature by about 20 °C improves boiler efficiency by roughly one percentage point. Condensate and flash steam recovery return heat to the boiler. Refrigeration desuperheaters and condensers provide warm water (see dairy-refrigeration-cold-chain), and heat pumps can lift this heat to temperatures useful for CIP and process water. Compressed air heat recovery heats water or space. Evaporator vapour recompression (TVR and MVR) recovers latent heat within the evaporator (see evaporation-drying-dairy), and spray-dryer exhaust heat recovery preheats inlet air. CIP solutions can be recovered and reused (see cip-sanitation-hygienic-design), and heat from hot effluents can be recovered before discharge. Pinch analysis — matching hot streams that need cooling with cold streams that need heating across the whole plant — identifies the maximum practical heat recovery and the best network of exchangers.
Cogeneration, or combined heat and power (CHP), generates electricity on site with a gas engine, gas turbine or steam turbine and recovers the waste heat from the exhaust and cooling systems as steam or hot water for the process. Because a conventional power station wastes most of its fuel energy as heat, CHP achieves much higher overall efficiency, commonly around 70–85 per cent of the fuel energy used as electricity and heat together. For example, a CHP unit producing 1 MW of electricity at 35 per cent electrical efficiency uses about 2.86 MW of fuel, and if it recovers 45 per cent of the fuel energy as useful heat (about 1.29 MW), its overall efficiency is 80 per cent. Trigeneration adds absorption chillers driven by the recovered heat to provide cooling. CHP suits dairies with steady, simultaneous demand for electricity and heat over many hours, such as plants with evaporators and dryers; its economics depend on the price difference between gas and electricity ('spark spread'), grid connection rules and capital cost. Biogas from effluent treatment or whey can fuel CHP engines.
A heat pump uses a refrigeration cycle to move heat from a low-temperature source to a higher-temperature sink; its coefficient of performance for heating (heat delivered ÷ electrical work) is typically between about 3 and 5 for moderate temperature lifts, falling as the lift increases. Dairies have plentiful low-grade heat sources — refrigeration condenser heat, cooling water from product coolers, warm effluent, compressor heat, dryer exhaust — and large demands for warm and hot water, which makes heat pumps attractive. Combined systems can provide refrigeration and hot water from one machine, using both sides of the cycle. Natural refrigerants such as ammonia, carbon dioxide (transcritical cycles that suit water heating to high temperatures) and hydrocarbons are favoured. High-temperature heat pumps reaching 90–150 °C are becoming available and can electrify part of the steam load, which, combined with renewable electricity, is a major route to decarbonising dairy processing. The design must match heat source and sink in time, often with hot-water storage, and the economics depend on the ratio of electricity to fuel prices. Refrigeration aspects are covered in dairy-refrigeration-cold-chain.
Dairies need much of their heat at moderate temperatures — hot water for CIP and cleaning at 60–90 °C, boiler feed preheating, pasteuriser hot water — which solar thermal collectors can supply. Flat-plate collectors suit temperatures up to about 80 °C, evacuated-tube collectors reach higher temperatures with better efficiency in cold weather, and concentrating collectors (parabolic troughs, linear Fresnel and dish systems) produce higher-temperature water or steam for process heat. Solar heat is variable, so systems include storage tanks and are integrated to preheat water before conventional heating. A collector field's useful output can be estimated as area × solar radiation × collector efficiency: for example 500 m² receiving 5 kWh/m² per day at 50 per cent efficiency delivers about 1,250 kWh of heat per day. Solar photovoltaic panels on roofs or land, or bought through power purchase agreements, supply electricity for motors, refrigeration and lighting; their output matches daytime loads such as refrigeration, especially with ice-bank or chilled-water storage. Solar-powered bulk milk coolers are an important application in rural areas.
Dairy effluent, whey and other organic residues can be treated anaerobically to produce biogas, typically around 60–70 per cent methane, as described in dairy-effluent-environment and whey-dairy-byproducts. The methane yield is about 0.35 m³ per kilogram of COD removed, and the biogas can fuel boilers, CHP engines or be upgraded to biomethane. At farm level, biogas from manure provides cooking fuel and energy for chilling. Biomass boilers burning agricultural residues, wood chips or briquettes replace fossil fuel boilers in many dairies, particularly in India and other agricultural economies, reducing fossil carbon dioxide emissions; they require fuel storage, handling, ash disposal and emission control. Wind power is usually purchased rather than installed on site. A renewable energy strategy combines efficiency first (reducing demand), heat recovery, and then renewable supply, often guided by corporate climate targets and national incentives.
Water conservation starts with measurement: sub-metering major users (CIP, boiler house, cooling towers, product areas, washdown), water balances that reconcile inputs and outputs, and specific water consumption benchmarks (litres of water per litre of milk). Common savings include optimising CIP programmes (phase separation by conductivity, rinse water recovery, shorter rinses validated by testing; see cip-sanitation-hygienic-design); fitting hoses with automatic shut-off nozzles and using high-pressure, low-volume cleaning; repairing leaks and dripping valves; controlling cooling-tower blowdown by conductivity and raising cycles of concentration with proper treatment; returning condensate; using dry cleaning of floors before washing; and training staff. Product losses to drain are both a water-quality and a cost issue, and reducing them lowers effluent loads.
Dairies have an unusual water source: the water in milk itself. When milk or whey is concentrated or dried, the evaporated water is condensed as 'cow water', which, after polishing (often reverse osmosis, ultraviolet disinfection and sometimes activated carbon), can replace fresh water for boiler feed, cooling towers, CIP pre-rinses and, with appropriate approvals, more demanding uses. Reverse osmosis permeate from membrane plants is another recoverable stream. Treated effluent can be reused for non-product purposes such as cooling towers, gardening and floor washing where regulations permit. Water reuse follows a fit-for-purpose principle: each source is treated to the quality needed for its intended use and monitored, with clear separation of recovered water from potable systems. Some plants aim to be net water-neutral or even net exporters of water, and zero liquid discharge (ZLD) systems, which recover almost all water and leave only solids, are required in some water-stressed regions. Recovery of cow water and effluent treatment are covered further in dairy-effluent-environment, and water and wastewater principles more broadly in the sustainability track's water-wastewater-treatment.
Boilers and pressure vessels store large amounts of energy, and failures can be catastrophic. The main hazards are: low water level, which lets furnace tubes overheat, weaken and rupture (and can cause an explosion if cold water is then fed onto overheated metal); overpressure if safety valves fail or are tampered with; furnace explosions from ignition of accumulated fuel or gas, prevented by purging before ignition and flame-failure protection; corrosion and scale, which weaken pressure parts and cause overheating; and scalding from steam and blowdown. Pressure vessels such as air receivers, steam-jacketed kettles, autoclaves, retorts, deaerators and refrigeration receivers carry similar risks. Safety depends on design to recognised codes, correct installation, safety devices, water treatment, inspection, trained operators and maintenance.
Boilers are among the most regulated equipment in industry. In India, boilers are regulated under the Boilers Act and the Indian Boiler Regulations, which require registration of boilers, inspection and hydraulic testing at registration and periodically by government boiler inspectors, issue of a certificate to operate up to a set pressure, and operation under the charge of certified boiler attendants or operation engineers, depending on boiler size; unfired pressure vessels and gas cylinders are regulated through rules administered by the Petroleum and Explosives Safety Organisation. In the United States, the ASME Boiler and Pressure Vessel Code governs design and construction, with jurisdictional inspection by states. The European Union regulates pressure equipment through the Pressure Equipment Directive, with national rules for in-service inspection. Common requirements across systems are: design and fabrication to a code; certified safety valves set and sealed below the design pressure; periodic inspection and testing; trained, certified operators; records of operation, water tests and blowdown; and investigation of incidents. Daily checks include water level gauge blowdown, low-water cut-out testing, safety valve checks at prescribed intervals, and water chemistry.
Many dairy vessels operate under pressure or vacuum and need the same discipline as boilers. Steam-jacketed kettles and vats, plate and tubular heat exchangers, sterilisers and retorts, air receivers, CO2 and nitrogen tanks, ammonia receivers and evaporator bodies are designed for stated pressures and temperatures, carry nameplates with their design data, and are protected by relief valves or bursting discs sized for the worst credible case. Vessels operating under vacuum must withstand external pressure and can collapse if designed only for internal pressure, a hazard when tanks are cleaned with hot solution and then cooled with closed vents. Hydraulic testing at a pressure above the design pressure, non-destructive testing of welds and thickness checks are used in initial certification and periodic inspection. Before maintenance, vessels and steam lines are isolated, depressurised, drained and locked out under a permit-to-work system, because residual steam and hot condensate cause serious burns. Operators must never gag or alter safety valves, and any modification to a pressure system requires review by a competent person.
A student uses this subject to name boiler mountings, calculate boiler efficiency, blowdown, flash steam, power factor correction and energy savings, describe water treatment and compressed air systems, and explain energy audits and safety rules. It supports AICE Dairy Engineering and AIEEA-PG group 18 questions.
A utilities engineer five years in runs the boiler house, water treatment, compressed air and electrical systems; tunes combustion, surveys steam traps and air leaks, manages condensate return and power factor, keeps boiler and pressure-vessel records for inspectors, and prepares energy and water reports. This subject gives the reasoning and calculations behind each task.
A plant head or engineering director decides on fuel switching, CHP, solar and biogas investments, energy and water targets, and compliance with boiler, electrical and environmental rules, balancing cost, reliability, safety and climate commitments.
A professor or research director works on process integration, heat pumps and renewable process heat, water reuse, and energy modelling for dairy plants, and teaches and examines dairy engineering topics on utilities.
This manual does not yet give: steam tables and detailed pipe and trap sizing; national water-quality limits for boiler feed and process water; detailed electrical system design; the current text of boiler legislation in each country (including any recent revisions in India); and quantitative energy benchmarks for dairy products. Efficiencies, temperatures, percentages and example costs are representative and should be checked against current data.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.