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Power Plant equipment protection with Nitrogen inert gas

Posted on: 15 Jul, 2013   |   With: 2 Comments
Category:  Gas Generation, Nitrogen

Over the last decade, several hundred power plants have come up or are in different stages of implementation and commissioning over the next 3-4 years. While a major chunk of these power plants are being constructed by major Indian Government entities such as NTPC and individual State Electricity Boards, many of these power plants are also being implemented by private companies which have been granted licenses by the Indian government for building and running these power plants.

One major cause of concern for many of these power plants is the supply crunch of fuel materials such as coal and gas. In cases where fuel availability challenges are experienced, many power plants are forced to idle their power plants or do a complete shutdown for several days and weeks at a stretch.

During these periods of prolonged idling or shutdowns, many of the power plant equipments such as Boilers, Turbines, Power cycle piping, Fuel Supply piping and other major BOP equipments have to be “preserved” to avoid major issues such as corrosion due to contact with air.

For these preservation activities, many power plants use dry Nitrogen gas. If the idle periods or shutdowns are periodic in nature, with not a high frequency, power plants earlier could rely upon Nitrogen being purchased in cylinders for these intermittent requirements.

However, as the frequency of these shutdowns has increased in the recent past owing to severe fuel supply challenges, the cost of Nitrogen procurement itself has gone up a lot. Many power plants are now seriously contemplating implementing on-site Nitrogen generators to avoid reliance on Nitrogen cylinder vendors. By purchasing and implementing a small Nitrogen Generator, power plants become self-sufficient and also are able to utilise this Nitrogen gas directly where it is required.

Nitrogen gas generators such as those supplied by MVS Engineering are very compact units that only require dry compressed air as the inlet source. Nitrogen is produced directly from the compressed air and delivered at pressure ranging from 8 to 12 barg.

Nitrogen produced from MVS gas generators is very dry with dew point below (-) 40°C. Such dry gas is very desirable in a power plant since dry gas prevents corrosion.

The cost of Nitrogen production is very low, around Rs. 3/- per cubic meter. When compared to Nitrogen delivered in cylinders, which costs around Rs. 15/- per cubic meter, one can easily see why even economically it is beneficial for power plants to generate their own Nitrogen on site.

We now explain the technical aspects of equipment preservation and demonstrate with a short example.

HOW TO PURGE, PRESERVE EQUIPMENT

Any equipment presently with and part of the normal atmosphere, when needed to be purged and preserved with Nitrogen gas requires the following:-
1. Purge the entire volume, minimum 6 times, displacing Air and replacing with Nitrogen.
2. Pressurize the equipment. A minimal pressure is required, and even 300 mm wg (0.003 kg/cm2g) is sufficient in most cases. Lesser maintained pressure will mean lower leakage rates through shaft/s and other non gas tight joints.

Take for example a 600 MW Generator. It has a 90 m³ internal volume. Therefore it needs 6 x 90 = 540 nm³ Nitrogen gas for initial purging. You can close all openings, flanges etc. and feed gas from a lower side flange on one side, and relieve the Air / Nitrogen from a flange (with partially closed valve which will help maintain back pressure also) on diagonally opposite side. Using a Nitrogen generator of 5 nm³/hr capacity will complete the initial purge in 540 / 5 = 108 hours (And really, there is no hurry!). Usually for such equipment, at 300 mm wg pressure maintained the leakage rate will not exceed 0.2% of the space volume which works out to 90 x 0.002 = 1.8 nm³/hr. This example goes on to show that a 5 nm³/hr Nitrogen generator is good to handle even 3 nos. 600 mw generator units.

We offer two distinct types of Nitrogen Generators:

Membrane Nitrogen Generators –
suitable for purities up to 99.9%
Membrane Nitrogen Generators provide many benefits over other technologies such as low maintenance, very low cost of production. Membrane Nitrogen Generators are ideal for power plants since the purity requirement of Nitrogen is never above 99%.

(Stock image of a similar ZEN-Series Membrane Nitrogen plant with Air Compressor)

PSA Nitrogen Generators – suitable for purities above 99.9%
PSA Nitrogen Generators are robust systems for producing Nitrogen of 99.9% purity or above. PSA is a very mature technology and MVS is India’s largest PSA Nitrogen generator manufacturer having supplied over 1200 Nitrogen gas generators worldwide.

(Stock image of a similar PSA Nitrogen plant)

About MVS Engineering Limited

MVS Engineering is a turnkey supplier of Gas generation equipment for Nitrogen, Oxygen and Hydrogengases. Additionally, we also manufacture Air, Gas, Liquid Dryers and also Gas Purification systems. MVS is the largest supplier of gaseous Nitrogen, Oxygen and Hydrogen plants in India. Besides India, MVS also regularly exports it’s equipment to the Middle East, Africa, South East Asia and Europe.

MVS was founded in 1977 and has supplied over 7000 Skid mounted units worldwide. Read more about the company in the About Us section of our website.

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