Sunday, March 24, 2013

Manpower Planning for Concreting

Suppose on a project, one had to complete 1000 cum of concrete in a month, how should one plan the manpower for that.

Ofcourse productivity depends on the type of structure, but I am speaking of a general approach and not specific to a certain type of structure.

For a general concrete structure we can assume 0.1 ton of rebar per cum of concrete on the average.

So 1000 cum of concrete works out to 100 ton of rebar.

Based on site observations a barbender with 2 helpers does approx 0.4 ton of barbending,cutting and fitup in a day.
So 1 gang of barbenders ( 1 main barbender and 2 helpers) would do approx 10 tons of reinforcement work in a month ( assuming 25 working days)

Hence to do 100 tons of rebar in a month 10 gangs would be required.

For shuttering, we can assume that 4sqm of shuttering would be required per cum of concrete.
Hence for 1000 cum of concrete, 4000 sqm of shuttering would be required.

One carpenter with 2 helpers do approx fit up of 4.5 sqm of shuttering in a day.
So 1 gang of carpenters would do appox 112.5 sqm of shuttering in a month
Say 100 sqm in a month

So in order to compete 4000 sqm of shuttering in a month, 40 gangs of carpentars are required.

Wednesday, March 13, 2013

Key Construction Risks for a Power Plant

Generally all systems outside the boundary wall of a thermal power plant carries a huge construction risk.

These systems include:
1. Cross Country Pipeline for delivering the water to the thermal power plant
2. Transmission Line  for delivering the electricity produced at the plant to the nearest point in the grid
3. Railway Siding for delivering coal to the power plant

Generally the amount of risk is directly proportional to the length of system. For instance, a cross country pipeline of 60kms carries a much bigger risk than a cross country pipleline of 20kms.

Land acquisition is also a serious concern as there maybe more than 2000 individual land owners.

Hence a better strategy is run your cross country pipelines  parallel to the road or a national highway and offset it from the highway by 10 to 30 metres. Generally the land around the highways is owned by Highway Authority or other Govenment bodies and getting the ROW is much simpler. However this carries a huge risk, as there maybe plans to make the highway from 2 lanes to a 4 lane highway in a few years and you maybe asked to relocate your pipeline.

Additionally our pipleline may also be crossing local roads, national highways, rivers, canals, railway lines, other pipelines, petroleum pipelines etc. While finalizing the route of the cross country pipeline we must have a very clear strategy for overcoming all these challenges.

Monday, March 11, 2013

How many energy units are produced by Power Plant in a single day

The electrical meter installed at our home measures energy units in KW-hr.
On the average, we consume about 300 units per month in non summer months (no AC), so really we are consuming about 300 KW-hr of electricity per month.

Say an average of 10 units per day.

So how many KW-hr does a power plant of of 300 MW size produce ?

Per day the power plant would produce = 1000 X 24 X 300 units =  72,00,000 units

However, the power plant would consume some of the power produced by it to run its own auxiliaries such as the coal handling plant, boiler feed pump, fans , pumps etc.

Hence on the average, auxiliary consumption is approximately 7% of the generated power for a unit of 300 MW sizing.

So the gross exportable power of the plant is 0.93 X 72,00,000 = 66,96,000 units

Further, we also need to consider the Plant Load Factor as the power plant would not be running contionously throughout the year.  It may have to take shutdowns for maintenance,  non-availability of coal, grid failures etc.

An average Plant Load Factor to consider for a new plant is 0.85 

So the net exportable power produced by a unit of 300 MW per day is 0.85 X 66,96,000 = 56, 91, 600 units per day.

If this plant was supplying power to only residential houses, then theoretically this power plant could power 5,69,160 houses considering an average of 10 units consumed by single house per day.

However in reality the Transmission, Distribution and Theft Losses in India are very high to the tune of 40 percent and this is where real change in policy is required.

Monday, September 26, 2011

Coal Handling Plant

Coal can be bought to the power plant via trucks or train or ship if power plant is located near sea.
The most common way to bring coal is by train.

Generally a railway track needs to be laid from the nearest railway station to the power plant. The train wagons are automatically unloaded using a wagon tippler mechanism and the unloaded coal is stored in an underground bunker. This coal is then conveyed to the crusher house using belt conveyor system. In the crusher house coal is crushed to around 25mm size. The crushed coal is then stored in coal stockyard using a mechanism called stacker-reclaimer. The coal is further conveyed to the ball mill via belt conveyor system. In the ball mill coal is pulverized to a powder form. This powder form is conveyed to the coal burners of the boiler using hot air which also dries the coal.

Generally speaking, about 0.5 T/hr of coal is required per MW unit size. So if you had a 200 MW unit, then 100 T/hr of coal would be required.

For 24 hours, you would need 2400 T of coal

One train carries appox 3000T. of coal. So 1 train of coal would be required to unloaded per day.