Fig. 1 - Start-up curves of a modern medium-speed gas engine. These are direct screenshots from engine control systems and were made during tests of a rapid start-up of a medium-speed gas engine operating in island mode. The top diagram shows a case of linear loading, while the bottom one involved pre-programmed load steps. In both cases start-up duration (40 and 41 seconds respectively) is measured from the start command until full output. Testing was performed in island mode.
Gas engines, come of age
But not long ago, gas-fired engines suffered a major drawback in terms of very delayed start-up timing – at times as high as 10 minutes. But recent years have seen huge progress on this front. Now these state-of-the-art gas engines can be started and brought to full power in considerably less than one minute of the starting order, ushering them into the world of emergency power supply.
In Figure 1, there are some exemplary and representative start-up sequences obtained during actual engine tests performed by Wärtsilä.
Gas engines have also taken care of the issue of fuel storage. Recent years have seen emergence of small-scale affordable gas storage technologies, especially in the form of liquefied natural gas (LNG). As a matter of fact, small-scale LNG storage and regasification plants are so reliable and safe that they are currently being installed on passenger ships. (Figure 2)
Clearly, modern gas engines hold enough power to become a potent alternative to diesel generators. However, gas engines go far beyond merely providing an equivalent solution. Restricting carbon emissions is very important amid growing environmental concerns. And adopting gas engines is the need of the hour as natural gas is the cleanest of all fossil fuels. Using gas means less CO2, which in turn means corporations can reduce their carbon footprint besides reducing costs. (Figure 3)
This means operating the generating sets continuously instead of relying on electricity grids would have a positive effect on the carbon footprint of the data center.
Fig. 2 - MS Viking Grace, a cruise ferry powered by
liquefied natural gas, has been safely carrying
passengers since January 2013.
Fig. 3 - Carbon footprint of different sources of electricity.
Note that generating power with on-site natural gas power
plant has lower footprint than the grid electricity.
The real power
That modern gas engines are the future of emergency power back up systems, has been established beyond doubt. But gas engines are not merely futuristic alternatives to diesel generators. In fact, gas engines are the game changers – because they can go beyond emergency.
Once an emergency power generation system is built using a solution that is neither legally nor technically restricted from operating beyond emergencies, there are two essential ways of using this capability:
- Self-generation
- Merchant operation
Self-generation model
This model shifts the source of primary power from the electricity grid to the emergency power generation facility. If a data center has a power-generation facility that can be operated continuously on an inexpensive fuel with very low emission footprint, then it may very well be used as a primary source of power.
This would make the local power plant the primary source of electricity, while the grid functions as a backup. This approach protects the data center operator from higher power costs and reduces carbon footprints too.
Data center operators can generate additional revenue as data centers do not operate on full design load. That time can be used to generate additional power & sell it to the electricity market along with the spare and redundant capacity of power plant. (Figure 4)
Fig. 4 - The self-generation model for a gas-fired
data center power plant.
Merchant plant concept
Unlike the self-generation model, in this case the gas-fired power plant can be used only as an emergency back-up power source while operating independently as a merchant generating station co-existing with data center and selling its production to external customers. In the event of any disruptions in the grid power supply, it would automatically switch to the emergency power supply mode. This might be a preferred approach for markets with high electricity cost. (Figure 5)
With the phenomenal advancement in gas engine technology and the advent of LNG solutions, there is no denying that the future of gas-fired engines, in data centers, holds immense potential.
Fig. 5 - Merchant plant model for the gas-fired data
center power plant.
Author: Adam Rajewski, Manager, Data Center Technology, Wärtsilä Enery Solutions,
mail: adam.rajewski@wartsila.com
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