Hotel Engineering Notes- Gas

GAS

Heat Terms and units: Method of heat transfer:(For Specific Heat, Thermal conductivity, Calorie, Calorific Value (both Higher or Gross calorific value and Lower or Net calorific value), Ignition point, Combustion efficiency, Conduction, Convection and Radiation, please refer previous notes on Fuels in catering industry)

LPG and its properties: LPG is synthesised by refining crude petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground.

LPG
Advantages	Disadvantages
High efficiency and heating rate	Faint odours
High calorific value 27800 kcal/m3	Leakage
No smoke, complete combustion	Fire hazard
Clean, easy to use, portable, cheap	Accident prone
Residue & oil contamination is small	Explosion

 Liquefied Petroleum Gas is a predominant mixture of Propane and Butane with a small percentage of unsaturates (Propylene and Butylene).  LPG may be defined as those hydrocarbons, which are gaseous at normal atmospheric pressure, but may be condensed to the liquid state at normal temperature, by the application of moderate pressures. Although they are normally

 used as gases, they are stored and transported as liquids under pressure for convenience and ease

Additive in LPG to make it foul smelling for easy detection of leaks. Because LPG is odourless, it is not easy to detect leakages and hence a foul smelling additive is added. This chemical is a Sulphur-based additive called Ethyl-Mercaptan (CH3 CH2SH). This is obtained by reaction of ethylene (C2 H4) with Hydrogen Sulphide (H2S).

of handling. Liquid LPG evaporates to produce about 250 times volume of gas. To aid in the detection of atmospheric leaks, all LPG’s are required to be odorized. For identification of gas leakage, LPG is mixed with an obnoxious smelling gas dehydrated desulphurised traces of organic sulphites. LPG vapour is denser than air: butane is about twice as heavy as air and propane about one and a half times as heavy as air. Consequently, the vapour may flow

 along the ground and into drains sinking to the lowest level of the surroundings and be ignited at a considerable distance from the source of leakage. In still air, vapour will disperse slowly. Escape of even small quantities of the liquefied gas can give rise to large volumes of vapour / air mixture and thus cause considerable hazard. There should be adequate ground level ventilation where LPG isstored. For this very reason LPG cylinders should not be stored in cellars or basements, which have no ventilation at ground level.

Storage Requirements

All gas cylinders:

§ Shall not be stored in exits or egress routes.

§ Shall be stored within a well-ventilated area.

§ Shall not be stored in damp areas, near salt or corrosive chemicals, fumes, heat or exposed to the weather.

§ Shall be stored in an upright position.

§ Shall be secured with a chain or appropriate belt above the midpoint, but below the shoulder.

§ Shall be capped when not in use or attached to a system (if the cylinder will accept a cap).

§ Shall be kept at least 20 ft. away from all flammable, combustible or incompatible substances. Storage areas that have a noncombustible wall at least 5 ft. in height and with a fire resistance rating of at least 30 minutes may be used to segregate gases of different hazard classes in close proximity to each other.

§ Shall be stored so that cylinders are used in the order in which they are received.

§ Shall be stored so that gases with the same hazard class are stored in the same area. Inert gases are compatible with all other gases and may be stored together.

§ Shall not be stored longer than one year without use.

§ Shall be stored so that full cylinders remain separate from empty cylinders.

COMPRESSED AND LIQUEFIED GAS USE

The general “good practice” guidelines to follow when using gas cylinders and compressed gases are:

General Requirements:

Ensure that regulator pressure control valve is relieved (i.e. closed) before attaching to gas tanks.

Close valves on gas cylinders when a system is not in use.

Remove all pressure from regulators not currently used (by opening equipment valves downstream after the regulators are closed).

Shut-off valves must not be installed between pressure relief devices and the equipment they are to protect.

Use pressure relief valves in downstream lines to prevent high pressure buildup in the event that a regulator valve does not seat properly and a tank valve is left on.

Relief valves should be vented to prevent potential buildup of explosive or toxic gases.

Never allow flames or concentrated heat sources to come in contact with a gas cylinder.

Never allow a gas cylinder to become part of an electrical circuit.

Never partially open a tank valve to remove dust or debris from the cylinder inlet.

Never use cylinder gas as compressed air.

Pressurize regulators slowly and ensure that valve outlets and regulators are pointed away from all personnel when cylinder valves are opened.

Cylinders that require a wrench to open the main valve shall have the wrench left in place on the cylinder valve while it is open. Use adequately sized wrenches (12” long) to minimize ergonomic stress when turning tight tank valves. Never apply excessive force when trying to open valves. Cylinders with “stuck” valves should be returned to suppliers to have valves repaired.

Do not attempt to open a corroded valve; it may be impossible to reseal.

Valves should only be opened to the point where gas can flow into the system at the necessary pressure. This will allow for quicker shutoff in the event of a failure or emergency.

Use a cylinder cap hook to loosen tight cylinder caps. Never apply excessive force or pry off caps. Return to supplier to remove “stuck” caps.

Keep piping, regulators and other apparatus gas tight to prevent gas leakage.

Confirm gas tightness by using leak test solutions (e.g., soap and water) or leak test instruments.

Release pressure from systems before connections are tightened or loosened and before any repairs.

Do not use Teflon tape on compressed gas fittings where the seal is made by metal-to-metal contact. Use of Teflon tape causes the threads to spread and weaken, increasing the likelihood of leaks.

Never use adapters or exchange fittings between tanks and regulators.

Fluorescent light can be used to check for grease or oil in regulators and valves.

The objective of good combustion is to release all of the heat in the fuel. This is accomplished by controlling the "three T's" of combustion which are (1) Temperature high enough to ignite and maintain ignition of the fuel, (2) Turbulence or intimate mixing of the fuel and oxygen, and (3) Time sufficient for complete combustion.

Operation of gas burner: To operate LPG gas cylinder, the cylinder valve is first opened and then the appliance valve opened and lighted match / lighter applied to the burner head simultaneously. The gas ignites instantly and flame can be adjusted by the control knob. When not in use the cylinder valve is to be kept closed to ensure safety.

Low Pressure Gas Burner

         

Low-And High-Pressure Gas Burners. The important thing in all gas-burning devices is a correct air-and-gas mixture at the burner tip as shown above in the figure. Low-pressure burners using gas at a pressure less than 0.15 kg/ cm² (2 psi),are usually of the multi-jet type, in which gas from a manifold is supplied to a number of small single jets, or circular rows of small jets, centered in or discharging around the inner circumference of circular air openings in a block of some heat-resisting material. The whole is encased in a rectangular cast-iron box, built into the boiler setting and having louver doors front to regulate the air supply. Draft may be natural, induced, or forced.

In a high-pressure gas mixer, the energy of the gas jet draws air into the mixing chamber and delivers a correctly proportioned mixture to the burner. When the regulating valve is opened, gas flows through a small nozzle into a venturi tube (a tube with a contracted section). Entrainment of air with high-velocity gas in the narrow venturi section draws air in through large openings in the end. The gas-air mixture is piped to a burner. The gas-burner tip may be in a variety of forms. In a sealed-in tip type, the proper gas-air mixture is piped to the burner, and no additional air is drawn in around the burner tip. Size of the air openings in the venturi tube end is increased or decreased by turning a revolving shutter, which can be locked in any desired position. Excess air levels in natural gas burner is in the order of 5%.

Draft System

The function of draft in a combustion system is to exhaust the products of combustion into the atmosphere. The draft can be classified into two types namely Natural and Mechanical Draft.

Natural Draft

It is the draft produced by a chimney alone. It is caused by the difference in weight between the column of hot gas inside the chimney and column of outside air of the same height and cross section. Being much lighter than outside air, chimney flue gas tends to rise, and the heavier outside air flows in through the ash pit to take its place. It is usually controlled by hand-operated dampers in the chimney and breeching connecting the boiler to the chimney. Here no fans or blowers are used. The products of combustion are discharged at such a height that it will not be a nuisance to the surrounding community.

Mechanical Draft

It is draft artificially produced by fans. Three basic types of drafts that are applied are :

Balanced Draft: Forced-draft (F-D) fan (blower) pushes air into the furnace and an induced-draft (I-D) fan draws gases into the chimney thereby providing draft to remove the gases from the boiler. Here the pressure is maintained between 0.05 to 0.10 in. of water gauge below atmospheric pressure in the case of boilers and slightly positive for reheating and heat treatment furnaces.

Induced Draft: An induced-draft fan draws enough draft for flow into the furnace, causing the products of combustion to discharge to atmosphere. Here the furnace is kept at a slight negative pressure below the atmospheric pressure so that combustion air flows through the system.

Forced Draft: The Forced draft system uses a fan to deliver the air to the furnace, forcing combustion products to flow through the unit and up the stack.

  

	COMBUSTION OF NATURAL GAS

 

  

                                                                                                                                               

				1 PART CO2 2 PARTS WATER VAPOUR 8 PARTS NITROGEN (11 PARTS EXHAUST)
	DRAFT FAN		GAS BURNER

 

 

HEATING APPLIANCE OR BOILER

               

               

	2 PARTS O2 8 PARTS N2 (10 PARTS AIR)				1 PART FUEL GAS

 

Manifold:

Gas manifolds provide a safe, cost-effective way of connecting and changing out compressed gas cylinders by simply eliminating the need to repeatedly handle the regulator during a cycle change-out. You can save yourself both time and money by using these manifolds. You will also be able to significantly reduce accidents caused by human error in changing out tanks. A gas manifold is a great way to increase your productivity, eliminate error, and enhance your gas delivery system.

1. An accessory system of piping to a main piping system (or another conductor) that serves to divide a flow into several parts, to combine several flows into one, or to reroute a flow to any one of several possible destinations.

2. A pipe fitting with several side outlets to connect it with other pipes.

A continuous supply manifold uses a pressure reducing regulator with diaphragm valves to create a compact gas delivery system that provides continuous gas flow. It uses two different gas sources, so when one source empties, it automatically draws from the second source. The first source can then be changed without interruption of the outlet pressure.

A header manifold provides a cost-effective way to connect multiple high-pressure gas cylinders to the same gas supply line. This design in gas manifolds can increase both gas storage capacity and flow rate, and also provides a means for a continuous supply of gas

A high-pressure inlet manifold is ideal for applications where gas consumption warrants one or two cylinders. It provided a safe, cost-effective means of connecting and changing out cylinders by eliminating the need to repeatedly handle the regulator.

Manifold configurations
To make the user use most of the allotted space for the system, two basic configurations are available-single row and double row.

Single row configuration: Here all the connections to the manifold of cylinder is done in a continuous straight line.

Double row configuration: Here the connections to the manifold occur on either side of the common line. It has two equal rows of cylinders with a common pipe running between the two rows. It requires support from either the ground up or suspended from above.

	GAS  MANIFOLD

 

 

GAS  MANIFOLD

               

A Bunsen burner, named after Robert Bunsen, is a common piece of equipment that produces a single open gas flame, which is used for heating, sterilization, and combustion. The gas can be natural gas (which is mainly methane) or a liquefied petroleum gas, such as propane, butane, or a mixture of both. A Bunsen burner has a needle valve. The hose barb for the gas tube is on the left and the needle valve for gas flow adjustment is on the opposite side. The air inlet on this particular model is adjusted by rotating the barrel / collar, thus opening or closing the vertical baffles at the base and so controlling the flame.