Any source of heat energy is called fuel.
The material which is burnt to produce heat is known as fuel. For example, wood, coal, domestic gas (LPG), kerosene, & petrol, are used as fuels in homes, industries & for transport. Most fuels are carbon compounds with hydrogen. When a “fuel is burnt”, it combines with oxygen in air to form carbon dioxide & water vapour & a lot of energy (heat & sometimes light”) is produced during this process.
There are two types of fuels:1. Primary Fuel. Occur is abundance in nature & used in natural form e.g. Coal, wood, peat, etc.
2. Secondary Fuel: Require some refining or processing or mixing. E.g. petrol. Kerosene, diesel, charcoal, coke, etc.
Other form of classification is:• Solid e.g. coal, wood.
• Liquid e.g. petrol, diesel
• Gaseous e.g. LPG, CNG.
• Un-Conventional fuel e.g. solar energy, biomass.
SOLID FUEL- Advantages
1. Low maintenance cost
2. Easily available.
3. Thickest type of fuel.
4. No expert required to take care.
1. Requires space.
2. Heat cannot be controlled.
3. Pollutes the environment.
4. Causes health hazard.
5. Ignition time is high.
6. More labour required to operate.
7. Not eco friendly.
LIQUID FUEL -ADVANTAGES:
1. Flow can be regulated.
2. Production of energy is instant.
3. Readily available.
4. Not as dirty as solid fuel.
5. More friendly.
1. Require space.
2. Lot of care to be taken.
3. Releases pollutants.
4. Sources are not reliable in terms of purity.
GASEOUS FUEL -ADVANTAGES:
1. Easy to handle
2. Saves lot of labour.
3. Controlled through regulators.
4. Very less pollution.
5. Instant fuel.
1. Transportation cost is high because of being highly volatile.
2. Regular check of equipment & supply line.
3. Lot of care by expect is required.
ELECTRICAL FUEL -ADVANTAGES:
1. Easy to operate.
2. Fuel is clean.
3. No storage required.
4. Efficiency is good.
5. Eco friendly.
1. Experts required to handle the equipment.
2. Chances if short circuit.
3. It is costly.
4. Risk of shock.
5. Cost of maintenance is high.
ENERGY RESOURCES – FOSSIL ENERGY RESOURCES:
OIL: Oil represents almost 40percent of the total energy consumption. Oil may be used in many products; heating oil is only one of them. Other products include natural gas, solvents, gasoline, kerosene, diesel, lubricating oil, & residue.
COAL: The second most commonly used source of energy for industry. Some large institutional complex utilizes coal to produce electric energy, with heat as a secondary output (co-generation). Coal is also used widely as cooking fuel in the hotel industry. Coal is one of the most abundant fossil fuel reserves on the earth. The heat value of coal is derived from its carbon content.
1kilogram of carbon(c), when combined with sufficient oxygen (O2) produces carbon dioxide (CO2) & will liberate 14,000 btu per pound (9050 watts per kilogram).
The major classifications of coal are:-Anthracite- Low sulphur content & high heat value.
Bituminous - High in sulphur & with a high heat value.
Brown Coal - Very low in sulphur & with medium heat content.
Lignite - Low sulphur & a low heat value.
Other fossil resources that are available in nature & could be used in future are shale oil, synthetic oil from coal, petroleum from biomass resources.
GasesGas energy resources include natural gas (NG), liquid natural gas (LNG), liquefied petroleum gas (LPG), & synthetic natural gas (SNG).
Natural gas & LNG
The primary source of heat in natural gas is methane (CH4). When methane is combined with oxygen (contained in air), the by products are carbon dioxide, water vapour, & heat but no pollutants. It is therefore an ideal source of energy. Natural gas provides about 1000Btu per cubic foot (1035 watts per cubic meter).
Liquid natural gas is obtained when natural gas is placed under very high pressure. Some LNG is produced when oil is refined.
Liquefied petroleum gases are primarily propane, butane, and isobutene & are usually extracted from NG. LPG is an ideal substitute for NG since gas burning equipment can consume either NG or LPG with very simple adjustments in equipment.
Synthetic natural gas can be produced from either petroleum products or coal. Coal or petroleum products can be used to produce naphtha, the primary source of heat for SNG.
Electricity:It is the cleanest fuel, controllable, with easy heat adjustment and requiring no storage space. It can be used efficiently for roasting, baking and toasting than for boiling and frying. However, it is often plagued with power cuts and interruptions. Insulation costs for electric equipment are higher than gas, owing to the costly switchgears required.
NUCLEAR ENERGY:Nuclear energy can be obtained by fission or fusion. Fission requires the splitting of the uranium atomic nucleus, which results in the release of large amounts of energy. Fusion is the union of automatic nuclei, resulting in the release of enormous quantities of energy.
SOLAR ENERGY:-Presently solar collectors provide temperature of 110 to 200°F (43.3 TO 93.30°C).
Most building heating systems in use today require much higher – temperature energy resources. So far, the greatest use of solar energy has been for domestic & swimming pool water heating.
Basic solar energy System-
Solar energy systems are classified as passive or active. Passive systems do not have mechanical components. A structure is built to utilize solar energy, to capture it for immediate warmth, & to store it for moderate night time temperatures.
Passive solar heating can be as simple as having many south facing windows & few windows on other sides of the building. Building & overhang or installing awnings on the south side will prevent unwanted heating in the summer. Variations on passive heating include:
Installing brick in front of windows which is heated during the day & re-radiates the heat as night.
Installing a wax-filled half –height wall in front of the windows which melts during the day & solidifies at night giving its heat to the inside of the building.
Building a porch or sunroom with a south facing glass front.
Building glass over a south –facing brick wall & circulating the heated air into the building.
Installing solar-wall siding on the south side of the building. This siding has small holes so that air is drawn into it & heated. The hot air is then circulated into the building.
Active system requires some type of electromechanical device to capture, concert, utilize, & store energy. These are costly systems. The system must have some type of solar cell, or receiver. The more common cell are flat- plate thermal collectors that heat up fluids, water or air.
The most effective active solar heating method is to heat a fluid in solar collectors. To prevent freezing at night, the fluid that is circulated to the collectors is generally a mixture of water & (non-toxic) antifreeze. A large tank of water is then heated with a heat exchange taking the heat from the water – antifreeze mix & transferring the heat to the water in the tank.
Heat is difficult to store for very long, but easy to store overnight. Heating a large tank of water is one way to store heat. Solar cells can also be use to convert solar energy directly to electricity, which has instant utilization. Electric energy can be conveniently stored in batteries for future use. These direct electric energy conversion systems are called photovoltaic systems.
USING THE FUELS:
Fuels are the sources of heat energy. It is the energy that the hospitality industry depends on in more ways than most people realize. People are aware of basic heating functions, such as heating buildings, heating water & cooking food. Some even associate heat with refrigeration & air cooling. However, heat is also required to transport customers to & from hotels. Internal – combustion engines, jet aircrafts & diesel trains depend on heat energy resources. Sanitation programs are still highly dependent on heat.
Many people use the terms & temperature interchangeably. Some may associate high temperature with heat & low temperature with the lack of heat. This impression is generally correct. More precisely, heat must be associated with quantity, while temperature is related to the intensity or quality.
Heat energy is measured in British thermal unit (BTU) or watt in standard international unit (SIU) heat measured in kilocalories.
Heat can be defined as the amount of heat required to increase the temperature of 1 kilogram of water by 1o C is equal to 1 Kilocalorie (1.16watt). A BTU is the amount of heat required to increase the temperature of 1 pound of water by 1oF.
There are two primary temperature scales, Fahrenheit & Celsius. Temperature scales are a function of boiling & freezing
Points of water at sea level. Water freezes at 32 degree F & 0 degree C & boils at 212 degree F & 100 degree Celcius.
Converting Celsius (t c) to Fahrenheit (t F) t F = (9/5) x (t c) + 32
TYPES OF HEAT:
SENSIBLE HEAT:Heat that increases the product temperature is called sensible heat. When the temperature of a product decreases the sensible heat has been removed. Basically, sensible – heat changes can be measured by using a thermometer.
The amount of increase or decrease in the temperature of a product depends on a product thermal property, the specific heat, & its weight. The specific heat is the amount of heat required to increase or decrease the temperature of a product one degree for each unit weight of the product.
Latent heat:-The critical temperature at which an object changes its state i.e. freezing point or boiling point is associated with latent heat.
There are several types of latent heat fusion, vaporization, condensation, & sublimation. The latent heat of fusion is the heat required either to melt or to freeze a produce at a given temperature, its freezing point. The latent heat of vaporization is the heat required to vaporization is the heat required to vaporize a product at a given pressure & temperature .its boiling point.
The latent heat of condensation is the heat that must be removed from a vapour to condense it to a liquid at a specific temperature & pressure. The latent heat of vaporization equals the latent heat of condensation at the same critical temperature & pressure. Some products proceed directly from the solid to the gaseous state, for example, dry ice at sea-level
Pressure, this is called latent heat of sublimation.
THERMAL AND CALORIFIC VALUE:For various fuels thermal & calorific value are shown in following table:
|calorific values of different fuels|
ENERGY REQUIREMENTS FOR COOKING FOODFOOD DATA:
WEIGHT: 4.54KG of fresh beef.
Specific heat: 0.87
Initial temperature: 4.4 degree Celcius
Average final temperature: 71.1 degree C, this means that the outside product temperature will be about 104.4 degree C & the interior product temperature will be 60.0 degreeC.
Product losses: There will be close to a 30 percent product loss made up of dripping & volatile losses. The amount of each depends on the processing technique. It will be assumed that half the losses will be volatile & half drippings. Dripping losses include product moisture & fat losses. The heat requirement of these losses are essentially latent – heat requirements.
The volatile losses are a direct latent- heat process as product moisture is changed to vapour or gas. The normal latent heat of vapour or gas. The normal latent heat of vaporization is very close to 712 watts per kg of volatile loss. The drip latent –heat requirements are essentially the energy requirements to change the beef fats from the solid to the liquid state. The typical latent-heat requirements are close to 38.8 watts per kg of product fat.
OTHER PRODUCT HEAT REQUIREMENTS:When meat is cooked, its proteins are broken-down. This also represents a latent heat requirement. The energy requirement for protein breakdown is about 64.7 watts per kg of protein. Once meat protein is broken down the energy requirements is 0 when the product is reheated, whereas the fat latent – heat requirements are retained when meat is reheated. As the product cools, liquid, fat still present in the meat changes back to solid state from liquid state, thus releasing heat back to the product (keeping it warm) even when it is removed from the source of heat.
|heat requirement calculation|
PRECAUTIONS WHILE USING GAS AS FUEL IN HOTEL INDUSTRY:
We take as many precautions as we can to make every room in the house as safe as possible. But special precautions must be taken in the kitchen. Most accidents that happen at home take place in the kitchen. Therefore adequate measures must be taken for kitchen safety. Since cooking gas are used in the kitchen, fire safety precautions are a must.
All working in kitchens must follow kitchen safety measures carefully, especially while cooking in the kitchen. Following these safety measures might save your life in an emergency. Here are a few safety tips, for fire safety while using cooking gas.
• Once you have completed cooking, make sure that you have turned off the stove and other appliances in the kitchen. Especially so before you lock the house and leave.
• LPG or cooking gas is actually a colourless, odourless gas. An artificial odour is added to the gas, so that the consumer can smell it, in case of a leak and take appropriate measures to seal the leak.
• Do not repair gas appliances by yourself. Get a professional to repair it.
• Take the lighter in one hand and then ignite the stove, instead of, opening the knob completely and then igniting.
• Get all gas appliances serviced regularly.
• Do not tamper with the safety valves for any reason.
• Use gas appliances that are approved and are of good quality. Ensure that all the parts have proper certification.
• If you smell gas in the kitchen, when the stove is not in use, turn off the cylinder/regulator immediately. This will cut off the gas supply and an accident may be averted. Open all windows and doors of the kitchen, so that there is adequate air supply. Do not turn on any electrical appliance in the kitchen at this time.
LPG GAS BURNER
Low pressure burner’s heat output is 12000 BTU/Hour. High pressure burner heat output is 60000 BTU/Hour. Although the burners differ in form, the principal parts are similar.
• Mixer Head: It mixes the gas and primary air, by carrying an air shutter and an opening for the gas orifice. The function of gas orifice is to allow gas in mixer head as a fine jet, moving at the velocity of 30-50 m/second.
|LPG gas burner|
• Gas Manifold: It connects the burner with LPG cylinder. It is the simple horizontal pipe through which the gas flows from the fuel line to different orifices of the burner.
• Burner Valve handles: These are attached to the manifold which directs the gas through orifice and mixer head into the burner.
• Primary Air Shutter: It allows primary air in the mixer head. Forced through the orifice at a velocity of 30-50 m/sec the gas develops sufficient suction to draw air through the partly open shutter.
• Venturimeter/Mixer tube: The air called as primary air mixes with the gas in this tube. Its smooth finish increases the injection of primary air and gives a clean, sharp flame.
• Cast Iron Burner: Its rough surface causes gas turbulence. The gas air mixture now flows through the ignition part on the side of the burner head.
• Gas Valve: It controls the gas supply to the burner.
• Knob/Valve handle: It controls opening of the valve viz. shuts, shuts fully or half.
PRINCIPLE OF BUNSEN BURNER
A Bunsen burner is a common piece of laboratory equipment used for heating, sterilization and combustion.
A common misconception is that German chemist Robert Wilhelm Bunsen invented the Bunsen burner. Although it is named after him, it is actually an improvement made in 1855 by his laboratory assistant, Peter Desaga, on an earlier design by Michael Faraday. The improvement is called a Tirrel Burner. The main difference between these burners is the gas control valve on a Tirrel Burner and the improved structure of the Tirrel Burner. Most Bunsen burners are in fact Tirrel Burners.
A Bunsen burner with needle valve. The hose barb for the gas tube is facing left and the needle valve for gas flow adjustment is on the opposite side. Air inlet on this particular model is adjusted by rotating the barrel, thus opening or closing the vertical baffles at the base.
The device safely burns a continuous stream of a flammable gas such as natural gas (which is principally methane) or a liquefied petroleum gas such as propane, butane or a mixture of both. At the time of its invention, the Bunsen burner would have mostly burnt coal gas.
The burner has a weighted base with a connector for a gas line (hose barb) and a vertical tube (barrel) rising from it. The hose barb is connected to a gas nozzle on the lab bench with rubber tubing. Most lab benches axe equipped with multiple gas nozzles connected to a central gas source, as well as vacuum, nitrogen and steam nozzles. The gas then flows up through the base through a small hole at the bottom of the barrel and is directed upward. There are open slots in the side of the tube bottom to admit air into the stream via the Venturi effect, and the gas burns at the top of the tube once ignited by a flame or spark. The most common methods of lighting the burner are using a match or a spark lighter.
The amount of air (or rather oxygen) mixed with the gas stream affects the completeness of the combustion reaction in the flame. Less air yields an incomplete and thus cooler reaction, while a gas stream well mixed with air provides oxygen in an equimolar amount and thus a complete and hotter reaction occurs. The airflow can be controlled by opening or closing the slot openings at the base of the barrel, similar in function to a car's carburetor.
If the collar at the bottom of the tube is adjusted so more air can mix with the gas before combustion, the flame will bum hotter, appearing blue as a result. If the holes are closed, the gas will only mix with ambient air at the point of combustion, that is, only after it has exited the tube at the top. This reduced mixing produces an incomplete reaction, producing a cooler but brighter yellow flame, which is often called the "safety flame".
CONSTRUCTION OF AN INDUSTRIAL GAS RANGE
On gas models, the available cooking surfaces may include open burners, uniform heat tops, graduated heat tops, and griddles. Uniform heat tops include two equal-sized plates, each with its own burner and controls. Heat is supplied over the entire surface of each section. The graduated heat top is provided with two open rings in the center of each top directly over the burners. Some burners are easier to remove for cleaning than others, and the easier it is to clean, the more often it will be cleaned. The newest innovation in gas burners is a system that delivers a mixture of gas and air. Conventional gas burners rely on the air available around the burner to support combustion. The air/gas burner does not need ambient air to function properly, so it is surrounded by a set of rings that trap heat and deliver up to 50 percent more heat directly to the pots and pan. Such burners cook faster, use less gas, and keep the kitchen cooler.
Gas combination range/ovens are stoves that have both surface burners and an oven. Depending on their features, some gas range/oven units are quite complex. To understand how they work, let's look at the following areas.
The Control Panel
There are many variations of range/oven combination units. We'll describe the following controls and devices, their function, and the interaction they may have with other components.
In a non-electric oven system, the thermostat is right behind the knob you use to set the oven baking or broiling temperature. It senses the temperature inside the oven and signals the thermostat to provide or prevent further heating.
The clock is either electronic or mechanical:
• Electronic clocks have a lighted, digital readout. These are not usually repairable; when they fail, you usually need to replace the whole clock.
• Mechanical clocks usually have three dials—the clock dial, a Start time dial, and a Stop time dial.
Some range/ovens have a keypad for setting all of the oven, broiler, timed bake, and self-cleaning times, and temperatures. These keypads can't be serviced; you usually need to replace them when a problem arises.
Selector Switch for Bake/Broil/Timed Bake, etc.
Gas range/ovens have at least one control switch for the oven/broiler. On some units, this is the same switch as the thermostat, on others it is a separate switch.
Many range/ovens have a light inside the oven. Sometimes a switch on the control panel lets you manually turn the light on. There may be a plunger-type of switch mounted to the frame of the stove that turns on the light when you open the door. Some units also have a range-top light with a manual On/Off switch on the control panel.
Self-cleaning Buttons or Switches
In addition to the clock controls for the self-cleaning feature, there may also be other related devices.
Gas Delivery (burner, oven, and broiler)All gas range top burners use a similar system of gas delivery. There's one control knob for each burner. It's attached to a small gas valve that's mounted right to a main gas line. As you turn on the valve, the gas flows through the valve into a "venturi" tube, which mixes the gas with air to create the proper mix for combustion. The mixture then flows into the burner itself, where the standing pilot light flame or the igniter ignites it. You regulate the flame size by adjusting the burner control knob. It restricts the amount of gas that flows through the valve.
Often the oven and broiler work in a similar way. The thermostat knob may be attached to a small gas valve that's mounted right to a main gas line. As you turn on the valve, the gas flows through the valve into a tube that is then attached to a safety control valve. The safety control valve doesn't allow gas to flow through to the burner unless there is an ignition source available. The ignition may be provided by a standing pilot light flame or by an electric igniter. When the gas flows and ignites, the flame stays lit until the thermostat senses the proper temperature and shuts off the gas flow.
With a digitally controlled system, there's no need for a mechanical gas valve. Instead, the digital circuitry sends the signal straight to the safety valve.
The Area Beneath the Cooktop
Many cooktops that have non-sealed gas burners let you raise the cooktop for cleaning and service. Many manufacturers often also place the model and serial number tag for the appliance beneath the cooktop. In addition, the individual burner gas valves and ignition components may be located here
The Interior of the Oven
The rack inside the oven holds the food to be cooked. The interior light bulb, the thermostat sensor, and, in some units the broiler components, are also located here.
The Area Behind the Broiler Drawer
This is where the safety valve, spark igniter, fuse, and other components are often located.
The Back of the Unit
Much of the wiring for a gas range/oven is located on the back of the appliance. The steel panels that cover the wiring protect both you and the wiring. Other components such as relays, self-cleaning switches, transformers, and terminal blocks are also behind the protective back panels.
Gas ranges are expensive; so initial selection is important, and the following points should be considered before being purchased:
• Overall dimensions in relation to available space.
• Weight with can the floor support the weight?
• Fuel supply is the existing fuel supply sufficient to take the increase?
• Drainage where necessary, are there adequate facilities? (e.g. for Chinese gas ranges)
• Water where necessary, is it to hand?
• Use does the food to be produced justify good use?
• Capacity - can it cook the quantities of food required efficiently?
• Time - can it cook the given quantities of food in the time available?
• Ease - is it easy for the staff to handle, control and use properly?
• Maintenance - is it easy for the staff to clean and maintain?
• Extraction - does it require extraction facilities for fumes or steam?
• Construction - it is well made, safe, hygienic and energy efficient and are all handles and knobs sturdy and heat resistant?
• Appearance - if equipment is to be on view to customers does it look good and fit in with the overall design?
• Spare parts - are they and replacement parts easily obtainable?
- Calorific Value: The amount of heat given by complete combustion of one unit mass of the substance.
- Kilo – Calorie: Heat unit in MKS system. It is the amount of heat required to raise temperature of 1Kg water by 1 degree Celsius.
- BTU : Heat unit in FPS system. It is the amount of heat required to raise temperature of 1 pound water by 1 degree Fahrenheit.
- Therm: It is equivalent to 100000 BTU.
- Latent Heat: Heat absorbed or given out by a substance while changing its state, without change in temperature.
- Specific Heat: Heat required to raise the temperature of one unit mass of substance by one unit degree temperature.
- Boiling Point: The temperature at which a substance changes its state from liquid to vapour without change in temperature.
- Melting Point: The temperature at which a substance changes its state from solid to liquid without change in temperature.
- Temperature: denotes the intensity of heat energy.
- Sensible Heat: The heat applied to a body , resulting in raise in its temperature.