FUEL AND INDUSTRIAL GASES

FUEL GASES

Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Many fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of potential heat energy or light energy that can be readily transmitted and distributed through pipes from the point of origin directly to the place of consumption

CLASSIFICATION OF FUEL GAS

Producer gas Water gas Coke oven gas Carbureted or oil gas Natural gas and LPG

Chemical reactions:C(s)+O2(g) (excess air) CO2(g) 2C(s)+o2(g) 2CO(g)C(s)+CO2(g) 2CO (g)C(s)+H2O(l) CO(g)+H2(g)CO(g)+H2O(l) CO2(g)+H2(g)

Methods of Production

PRODUCER GAS: Raw materials-

Coal or blast furnace coke Air

Quantitative requirements Basis: 100 Nm3 of producer gas Coke 20-25 Kg or coal 25-30 Kg Steam 8-10Kg Air 60-80 Nm3 Plant capacities:25000-250000 cubic metres /day

Composition: CO ,N2 ,H2 with steam

Principal use : Steel industry heating requirements (heat treat , coke ovens)

Process description: Steam and air mixture injected in bottom of a water cooled jacket of steel furnace equipped with a rotating grate to remove fusible ash. Solid fuel is added from hopper valve on top a furnace. Producer gas is cooled by passing through a waste heat boiler.

Major engineering problems: a) Design of suitable gas producer furnace

to : keep uniform fuel surface Provide adequate gas-fuel contact time at high

temperature Avoid clinkering and provide for proper fused

ash removal b) Addition of correct steam quantities to

supply net heat of reaction near zero on a continuous once- through process

MANUFACTURE OF PRODUCER GAS

WATER GAS Composition : CO ,H2

Principal use : Heating ,chemical synthesis Raw materials:

Bituminous, anthracite coal , or coke Quantitative requirements Basis: 100 cu m of water gas from C

C as coke 55kg

or C as coal 58 kg

Air 220 Nm3

Steam 80 kg Plant capacities : 250000-1500000 Nm3 /day

Process description: Regenerative process- older process consisting of two reactors one operates on blow period which heats carbon by reaction 2(a) , the other on a run period where endothermic reaction 2(d) occurs. The cycle of 4-6 minutes is divided as Blow or heat up - 35% Up run - 30% Down run – 33% Short purge up run - 2%

Reactors or generators or steel with refractory lining .If higher BTU gas is required an additional high temperature carburetor section is required for pyrolyzing oil spray and mixing .

Continuous process – newer process ,based on low purity grade oxygen. The correct ratio of steam , oxygen and coal is added to the reactor which yields approximately zero heat release, ash content greater than 30%

Major engineering problems: a) Designing suitable ash removal system for various grades of coal in continuous processing. b) Optimizing cycle for regenerative process

MANUFACTURE OF WATER GAS

Principal use COKE OVEN GAS

Composition : H2 ,CH4 ,CO : Heating , Chemical synthesis

Process description : Upgraded coal for coking purposes is fed

to a by-product coke oven which uses producer gas for heating the batch chamber to 1000 0C for 12-20 hours. Gas is removed continuously and put through a series of purification steps.

If NH3 synthesis gas is required , further purification including scrubbing with alkali to remove CO2 ,liquefaction to remove light hydro-carbons and finally scrubbing with liquid N2 to take out CO . The N2 for scrubbing and make up is obtained from a liquid air fractionation plant . The oxygen being used to purify pig-iron and make high grade steel by the Linz and Donowitz process.

Major engineering problems :

Obtaining suitable grades of coking coal in India . Washing , pre-roasting and solvent extraction are some of the schemes used.

Choice of scrubbing liquors for CO2 and CO.

SYNTHESIS OF COKE OVEN +NH3

NATURAL GAS

Principal use –heating ,chemical synthesis

Process description

Gas is pumped from natural gas and petroleum wells to drying units (absorption ,adsorption or refrigerated compression). separation of the heavy ends done by either absorption or liquefaction. Adsorption is not competitive for this operation

the natural gas ,containing over 95% CH4 with the balance as ethane next sent to purification units for removal of H2S and other sulphides . Various absorptions and chemical reaction methods are available with the ethanol amine absorption process in current favour.

Liquefied Petroleum Gases(LPG)

Principal use-heating ,chemical synthesis.

Process description these gases are byproducts from

natural gas separation plants and petroleum refineries. They consist essentially of purified propane and butane in various mixtures . The propane fraction only is supplied for residential fuel in northern winter climates because of its lower boiling point.

The ethanol amine absorption processe flow sheet indicates the possible physical steps used for separating moisture,H2S and petrol. Drying can be either by adsorption or refrigeration ;the heavy end removal by either absorption or refrigerated liquefaction .The choice depends on location and power costs.Natural gas as the overhead is stripped of H2S in an ETHANOL AMINE ABSORPTION PROCESS.

NATURAL GAS AND LPG TREATMENT