AVAILABILITY BASED TARRIF(ABT)

Availability Based Tariff (ABT) is a frequency based pricing mechanism for electric power. The ABT falls under electricity market mechanisms to charge and regulate power to achieve short term and long term network stability as well as incentives and dis-incentives to market participants against deviations in committed supplies as the case may be.

ABT Mechanism (Energy policy of India) is adopted in India (ABT Order dated January 2000 of CERC) and in a few other countries for pricing bulk power across various stakeholders. ABT concerns itself with the tariff structure for bulk power and is aimed at bringing about more responsibility and accountability in power generation and consumption through a scheme of incentives and disincentives. As per the notification, ABT was initially made applicable to only central generating stations having more than one SEB/State/Union Territory as its beneficiary. Through this scheme, the Central Electricity Regulatory Commission (CERC) looks forward to improve the quality of power and control the following disruptive trends in power sector:

• Unacceptably rapid and high frequency deviations (from 50 Hz) causing damage and disruption to large scale industrial consumers
•   Frequent grid disturbances resulting in generators tripping, power outages and power grid disintegration.

**The ABT scheme has now been expanded to cover the Intrastate systems as well.

What is availability?

'Availability', for the purpose of the ABT Order means the readiness of the generating station to deliver ex-bus output expressed as a percentage of its related ex-bus output capability as per rated capacity.

  How is availability calculated?

“Availability of thermal generating station for any period shall be the percentage ratio of average SOC for all the time blocks during that period and rated Sent Out Capability of the generating station”

Scheduling

• Each day of 24 hours starting from 00.00 hours be divided into 96 time blocks of 15 minutes each.
• Each generating station is to make advance declaration of its capacity for generation in terms of MWh delivery ex-bus for each time block of the next day. In addition, the total ex-bus MWh which can actually be delivered during the day will also be declared in case of hydro stations. These shall constitute the basis of generation scheduling.
• While declaring the capability, the generator should ensure that the capability during peak hours is not less than that during other hours.
•  The Scheduling as referred to above should be in accordance with the operating procedures in force.
•  Based on the above declaration, the Regional Load Dispatch Centre(RLDC) shall communicate to the various beneficiaries their respective shares of the available capability.
• After the beneficiaries give their requisition for power based on the generation schedules, the RLDC shall prepare the generation schedules and drawal schedules for each time block after taking into account technical limitations and transmission constraints.
• The schedule of actual generation shall be quantified on ex-bus basis, whereas for beneficiaries, scheduled drawals shall be quantified at their respective receiving points.
•  For calculating the drawal schedule for beneficiaries, the transmission losses shall be apportioned in proportion to their drawals.
•  In case of any forced outage of a unit, or in case of any transmission bottleneck, RLDC will revise the schedules. The revised schedules will become effective from the 4th time block, counting the time block in which the revision is advised by the generator, to be the 1st one.
•  It is also permissible for the generators and the beneficiaries to revise their schedules during a day, but any such revisions shall be effective only from the 6th time block reckoned in the manner as already stated.

ABT features

• ABT brings about enhanced grid discipline
• Economically viable power with right pricing
• Promote competition and efficiency
• Encourage use of Merit Order Dispatch / Economic Dispatch in India
•  Addressing grid disturbance issues
• Gaming and avoiding the same
•   Requires special meters, remote metering with open protocols and communication mechanisms to read meters timely
•    Software that is comprehensive to do calculations, address regulatory issues and modifications as per different Regulatory Commission requirements.
•      Interface options to various stakeholders in the ABT mechanism online to enable effective implementation and benefits to all
•     Capability of power producers to be able to control their cost of production as well as flexibility in operations

ENERGY & POWER CONVERSIONS

Power & Heat Units

1 MW = 1,000 kW

1 kW = 1,000 Watts

1 kWh = 3,412 Btu

1 kWh = 1.340 Hp hours

1,000 Btu = 0.293 kWh

1 Therm = 100,000 Btu (British Thermal Units)

1 Million Btu = 293.1 Kilowatt hours

100,000 Btu = 1 Therm

1 Watt = 3.412 Btu per hour

1 Horsepower = 746 Watts

1 Horsepower hr. = 2,545 Btu           

Heat & Energy Units

1 KJ = 1,000 Joules

1 MJ = 1,000 KJ

1 MJ = 1,000,000 Joules

1 KJ = .239005 Kilocalories

1 Joule = 0.23901 Calories

1 Calorie = 4.184 Joules

1 Kcal/Kg = 1.8 Btu’s/lb.

1 Million Btu = 252 Megacalories

1 Btu = 252 Calories

1 Btu = 1,055 Joules

1 Million Btu = 1,055 Megajoules

1 Btu/hour = .2519 Kilocalories/hour

1 Btu/lb. = 2.3260000 KJ/KG

1 Btu/lb. = 0.5559 Kilocalories/KG

Power Generation Units

1 MWe = 1,000 kW

1 MWh = 3,600 MJ

1 MWt (thermal energy) = Approximately 1,000 kg. steam/hr.

Natural Gas Units

1 Cubic foot of natural gas = 1,020 Btu (approx)

1 Therm = 100,000 Btu

1 Decatherm = 10 therms

1 Decatherm = 106 Btu

1 Decatherm = 1,000 cubic feet of natural gas (approx)

1 Decatherm = 0.974 Mcf at 1,026 Btu per cubic foot

1 Mcf = 1.026 MMBtu (approx)

1 Mcf = 1.026 Decatherm (approx)

1 MMBtu = 106 Btu’s

Mass Units

1 Metric ton = 1,000 KG

1 Metric ton = 0.9071847 short tons

1 Metric ton = 1.016047 long tons

1 Metric ton = 2,204.622 pounds (lb.)

Temperature

°C = (°F – 32)5/9

°F = (9/5)(°C)+32

SUPERCRITICAL BOILER

Supercritical Boiler

 1.        Operating Pressure >  225 Kg/Cm2,  It Is Called A Supercritical Boiler.

2.           The Most Techno-Economical Parameters For Supercritical Plants Envisaged Are:

Main steam Pressure	@ SH outlet  is 250 Kg/Cm
540 Deg.C	Main Steam Temperature At Sh O/L.
566 Deg.C	Hrh Temperature At Rh O/L.

3.          Improvement In Cycle Efficiency for above Parameters Is Of The Order Of 3%.

4.       There Are Two Types Of Water Walls  Arrangements In The Case Of  Once Through Boiler:

A)             Spiral Wound WW.

B)              Vertical Ribbed WW.

5.               Most Of The Once Through Boilers In The World Are With Spiral Wound WW.  This Arrangement Has The Advantage Of Equal Heat Absorption By All The Steam Generating Tubes.

     The Disadvantage Of This Arrangement Is That The Tubes Are Not Self-Supporting.  Hence, Extra Supports Are Provided To WW For This Arrangement.

  Typical Materials Used For Super critical Boiler

Elements Of Boiler	Material
Economizer	Carbon Steel
Water Wall	Low Alloy Ferritic Steel
Pressure Vessels (Separator, Drain Tank)	Low Alloy Ferritic Steel
Sh Tubes (Heating Area)	Austenitic Steel (Tp347h / Tp321h)
Sh Tubes (Non-Heating Area)	Medium Alloy Steel (T91)
Main Steam Pipe	Medium Alloy Steel (P91)
HRH Pipe	Medium Alloy Steel (Scmv28)

START UP IN THERMAL PLANTS

COLD START

1)           After Capital overhaul.

2)      After Annual overhaul.

3)     After any major rectification work like H2 leakage / T-G Bearing High Vibrations / Stator winding fault / Rotor earth fault.

WARM START

1)              After LTSH, SH Re heater tube leak rectifications.

2)              After H2  leakage - Rectification, After Auxiliaries like PA Fan / CW pump motor rewinding.

3)              Reserve shutdown due to High frequency, CW Sump level (River level) problem.

4)              Electrical faults like Surge Capacitor failure / Rotor earth fault / Stator Earth fault / GT Buchholzs.

5)              Coal shortage.

HOT START

1)              Economizer tube failure.

2)              Water wall tube failure.

3)              Turbine impulse line leakage.

4)              MS-Valves heavy gland leak.

5)              Generator X-r bushing oil leaks.

6)              Gland cooler gasket failure (leakages in condensate flow path) , Turbine lube oil cooler leaks.

7)              Cable flash over of Unit bushes / UAT etc.

8)              Small maintenance works on feed water line, de-Aerator etc. / small fire hazard

9)              Start up after fictions tripping (Governing System trouble / I&C trouble.

10)          Start up after trip out due to Mal-operation human error / Instrument error or relay / Protection, Momentary drum level / draft / vacuum.

The Health Risks of Burning Coal for Energy

Nitrogen oxides (NOx):

Nitrogen oxide plays a major role in the formation of ground-level ozone (or smog) in summer and contributes to fine particulate matter (or soot). Both smog and soot are linked to a host of serious health effects. Nitrogen oxide also harms the environment, contributing to acidification of lakes and streams (acid rain) and the haze that often shrouds our national parks and scenic vistas. 

Mercury (HG): 

 Mercury can cause severe nervous system problems in humans and wildlife. Especially vulnerable are developing fetuses, babies and children. Eating fish is one of the primary ways people ingest mercury, which accumulates in the tissues of fish and other animals. Texas is home to five of the nation's top 10 mercury emitting power plants.

Sulfur dioxide (SO₂): 

 Sulfur dioxide contributes to the formation of microscopic particles (particulate pollution or soot) that can be inhaled deep into the lungs and aggravate respiratory conditions such as asthma and chronic bronchitis, increasing cough and mucous secretion.

Carbon dioxide (CO₂) and Global Warming:

 Carbon dioxide does not directly impair human health but is the most significant greenhouse gas that contributes to global warming. The dangers of global warming include disruption of global weather patterns and ecosystems, flooding, severe storms and droughts. A warming climate will also extend the range of infectious diseases.

DUST REDUCTION METHODS IN THERMAL PLANTS

 The major methods used in coal mines and thermal plants to control dust pollution are  

•      Ventilation
•      Water sprays
•      Dust collectors

 I). Ventilation:

                 The ventilation methods provide the best use of air in the vicinity of workers and in the vicinity of dust sources. There are different methods

1. Dilution Ventilation:

 In this method it is used to provide more air and dilute the dust. Most of the time the dust is reduced roughly in proportion to the increase in air flow, but not always.

2. Displacement Ventilation :

In this method it is used to use the airflow in a way that confines the dust source and keeps it away from workers by putting dust downward of the workers.

II).Water Sprays :

There are 3 methods 

1. Wetting :

          By wetting of the coal adequate dust pollution can be controlled. Due to wetting the dust particles stay attached with surface of coal material. 

2. High pressure sprays:

This method improves spray by raising the water pressure which may further causes to raise the efficiency per unit use of water. In this case there is a chance to get reduced 30 to 40% dust pollution?

3. Foam:

  For dust control foam may be better than water. It provides dust reductions upto 20% to 60% compared to water. Foam also can produce similar results at lower water use that is the amount of water needed to make the foam is less than the equivalent water spray. Only drawback is high cost. 

III).Dust Collectors :

                  The dust collectors play a vital role in dust reduction in mining and coal plants of thermal power plants. Dust collectors range from low-volume filtration to high volume wet collectors is used in various locations such as conveyor areas, tunnels, crusher areas and bunker areas. For dust collectors properly designed to trap respirable dust, the filtration efficiency is usually quite high in the range of 90-95%. 

 

       Methods generally implemented in thermal plants

 

Location	Method implemented
Coal transportation	Wagons covered with tarpaulins
Wagon tippling	Spraying water
Conveyor streams	Dust collectors and sprinkling water
Crusher houses	Dust collectors
Bunkers	Dust collectors
Coal yards	Sprinkling water

COMPARISON OF VARIOUS SYSTEMS:

DUST CONTROL METHOD	Effectiveness (Low is10-30%, Moderate is 30-50%, High is 50-75%)	Cost and draw backs
Dilution Ventilation	Moderate	High
Displacement ventilation	Moderate to high	Moderate
Wetting	Moderate	Low
Foam	Moderate	High
Water high pressure sprays	Moderate	Moderate
Dust collectors	Moderate to high	Moderate to high

DESIGN REQUIREMENTS FOR CHP

            The sizing and selection of the vital equipment i.e., crushers,screens,paddle feeders etc. covered under the system shall be based on the following characteristics of coal and operation conditions :

1. Two conveyors must be established (1W,1S) for smooth running of plant.
2. Simultaneous running of both conveyors at rated capacity is essential.
3. Round the clock operation of coal handling plant is essential.
4. Coal delivered to the power station shall be of size :300 mm & below (Occasionally 1-2% coal of 400 mm lumps may be allowed.
5. H.G.I of the   coal shall be between 45 to 65.
6.  Moisture content in coal will vary between 12% to 15% (For design purpose 20% is considered)
7. The coal  may have max of 20% of shale and sand stone.
8. For volumetric computation the bulk density of coal shall be taken as 800 Kg/M3
9. All hoppers and tunnels provided with 2 No.  sump pumps (1W+1S)
10. The coal unloading ysystem shall be capable of unloading the rake within time.
11. The wagon tipplers shall be "ROTA SIDE " type and the angle of tippling is 150deg by     giving 60 deg angle to the side of the wagon for emptying the coal contents into the hopper.
12. The tippler designed to allow passage of BROAD GAUGE (1676 mm) track over tippler table. 
13. The Wagon tippler hopper shall have capacity of 3 wagons i.e.180 tons .
14. The steel grating of mesh size 300mm X 300mm over wagon tippler hopper.
15. Belt Weigher shall be designed for a range of 20% to 120% of rated capacity.
16. RING GRANULATORS type crusher shall be provided for sizing the input coal to (-) 20mm (from 300mm). 

COAL CONVEYOR BELT-PROTECTION

           The coal conveyor belts in coal handling plant of thermal plants are protected by following ways 

1). PULL CHORD (Manually Reset type) : 

               This is a emergency stop switch  shall be located on both sides of belt conveyors at a a spacing of 20 Mtr. along the walkways for the entire length of conveyor for emergency stopping of conveyor.

2). SWAY SWITCH : 

              This switch is of self resetting type and it shall be provided at a spacing of 45 Mtr to limit belt sway to permissible extent.

3).ZERO SPEED SWITCH: 

             This switch is non-contact 9Proximity ) type electronic switch.

4). CHUTE BLOCKAGE SWITCH : 

             This switch is of proven type and it shall be provided at a suitable height on each leg of the conveyors discharge chute, Vibrating Screens by pass chutes ,Crusher feeding chutes ,Tripper discharge and feeding chutes nearest skirt boards.

               Chute blockage switch shall trip the feeding conveyor in case of chute blockage and protect the feeding conveyor equipment.   

 

DESIGN OF STOCKPILES

        The stockpiles of coal will have adequate storage power plants for few days and the coal consumption shall be based on the Heat rate and Average GCV of coal received.

PLANT LOCATION              COAL STOCK (Requirement)

PIT HEAD                                    15 Days

LOAD CENTERS                         30 Days

COASTAL                                    30 Days                           

BELNDING OF COAL

            In any coal fired power plants the blending of "Ingenious coal" and "Imported coal" can be done in following ways 

A).We can convey Indian coal through one stream and Imported coal through another  stream which will get mixed while falling into coal bunkers.

B). We can stock Indigenous and Imported coal layers in stockyard.Before feeding by using dozers we can blend  and feed to the bunkers.

C).We can use one mill is separately for Imported coal and then adjust the mill parameters to achieve the optimum heat load of the burners.