8.0 Renewable energy

 

Renewable energy is useful energy that is collected from renewable resources. They are naturally replenished with the time. These are like sunlight, wind, rain, tide and geothermal heat. This type of energy source stands in contrast to fossil fuels, which are being used far more quickly than they are being replenished. Although most renewable energy is sustainable energy but some is not, for example some biomass is unsustainable.

Renewable energy often provides energy in four important areas:- 

·         Electricity generation, 

·         Air and water heating/cooling, 

·         Transportation,

·         Rural (off-grid) energy services.

 

Types of Renewable energy:-

1.       Wind Power

2.       Hydro Power

3.       Solar Energy

4.       Geothermal Energy

5.       Bio Energy

 In this article, we will discuss about Bio Energy.

Biomass is biological material derived from living, or recently living organisms. It most often refers to plants or plant derived materials. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel.

Types of Bio fuels:-

1.     Wood – dead tree, branches, tree stumps, wood chips etc.

2.     Plants – Bamboo, Sugar cane ( Bagasse), Rice straw & Rice husk, Corn, Miscanthus, Switchgrass, Hemp, sorghum etc.

3.     Biofuels can be converted to other useful form of energy.

·         Liquid - Biodiesel, Bioethanol

·         Gaseous - Biogas, Landfill gas, Synthetic Gas

Type of Biomass Boilers:-

Type	Process	Advantage	Disadvantage
Pile Burner	Biomass is dumped on piles in a furnace and burned with the help of combustion air coming from under and above the pile.	Fuel flexibility and the simple design	Low boiler efficiency and relatively poor combustion control.
Stoker Fired Boiler
i. Stationary sloping grate	Grate does not move, but the fuel burns as it slides down the slope.		Difficult control of the combustion process and the risk of avalanching of the fuel.
ii. Travelling grate	Fuel is fed on one side of the grate and has to be burned when the grate has transported it to the ash dumping site	Combustion control is improved, carbon burnout efficiency is also better
iii. Vibrating grate	Fuel is fed evenly on the whole grate. The grate has a kind of shaking movement which spreads the fuel evenly.	lower maintenance, Carbon burnout efficiency is further improved
Suspension fired boilers	Fuel is fired as small particles which combust while they are fed into the boiler.	High boiler efficiency	Lot of pre-treatment of the fuel is required.
Fluidized bed Boiler	Combustion air from below the boiler has such a high speed that the fuel becomes a seething mass of particles and bubbles.	Suitable for co firing different kind of fuels, Carbon burnout efficiency is very high, control NOx and SOx.	High fan capacity require

 Problems in biomass plant:

1.       Frequent tube failure – biomass contains high silica, which is come from pesticides (potassium) used during cropping.

2.       High extraneous matter in biomass ( sand and mud) causes tube fouling and frequent before drain.

3.       Carbon and dust coating of boiler tubes results lowering steam temperature.

4.       High moisture content – plugging and checking of closely spaced heating surface. Jamming of fuel feeder causes fluctuation in steam pressure and temperature. In rainy season effects the efficiency of plant.

5.       Degradation of biomass during storage in exposed, ambient wet atmosphere leads in loss of heat value of fuel.

Analysis of Coal Vs Rice husk as fired basis (For reference purpose only):-

Material	D- Grade Coal	E-Grade Coal	Rice Husk
Proximate Analysis, % on fired basis
Total Moisture	14.00	15.00	9.22
Ash	21.98	29.08	15.36
Fixed carbon	40.49	34.85	13.50
Volatile matter	23.53	20.07	61.92
Gross calorific value (GCV), kcal/ kg
As air dried basis	5229	4387	3790
Ultimate Analysis, % on air dried basis
Carbon	62.16	53.50	33.49
Hydrogen	3.66	3.18	4.60
Sulfur	0.56	0.62	0.31
Nitrogen & Oxygen ( By difference )	7.19	7.26	37.02
ash	25.26	34.18	15.36
Moisture	1.17	1.26	9.22
Crucible swelling Index	1	1
Chemical Analysis,  Fuel Ash, %
Al2O3	39.63	40.10	2.02
CaO	3.52	1.29	7.07
Fe2O3	5.38	1.10	0.98
MgO	0.22	0.18	1.64
TiO2	0.20	Absent	Absent
P2O5	0.16	0.20	0.25
K2O	0.58	0.59	0.60
SiO2	48.86	54.79	86.86
Na2O	0.69	0.67	0.10
SO3	0.03	0.04	0.05
Loss on Ignition	0.58	0.92	0.43
Undetermined	0.15	0.12	-
Ash Fusion Temperature for Coal in °C (Under Mildly Reducing Atmosphere)
Softening Temperature	1270	>1400
Hemispherical Temperature	1350	>1400
Fluid Temperature	1400	>1400