The well-documented changes in power markets and the associated pressures on power plants have given rise to a more pressing need for plant performance modelling.
Ed Naylor of Frazer-Nash spoke to Power Engineering International last week about the services such a consultancy can provide in assisting operators overcome the challenges to optimising their facilities.
Those challenge, in terms of improving efficiency and extending component life, have never been greater given the new demands on power technologies.
The introduction of the Capacity and Short Term Operating Reserve (STOR) markets bring new challenges for rapid starts, multià¢€‘starts per day and even open cycle operation. Stations were not originally designed for these types of operations, which are known to be more damaging to plant assets and impact on the flexibility, reliability and availability of them.
“One of the problems with renewables sources is that they can be intermittent and inflexible generating sources. So with the increase in that your conventional power stations, be it coal or gas, needs to be more flexible and what used to be a handful of starts in a year these days 250-300 starts in a year is not uncommon,” Naylor told PEi. “These plants were not designed for that and its putting a hell of a lot of stress on the system because of the loads that go through it during these starts.”
Frazer-Nash can thermodynamically simulate the operation of a power station offering that opportunity to improve efficiency and extend component life. Furthermore it can significantly reduce operational risks by simulating different operating scenarios and proactively, rather than reactively, planning for outages.
By way of example Naylor points to the case of a typical gas-fired power plant charged to cover the profitable peak in demand in the balance of the output of wind power, with a demand to have a fast start time.
“Just turning on the turbine generation generates all that power but it has impacts on other parts of the system be it bypassed lines, valves or condensers. Where we use performance modelling is we can look before the operator moves to a new operating philosophy and we can model what the impact is ” are these valves the correct size?, are they undersized?, are there any transient phenomenon we don’t normally see because of the ramping?”
“The issue could be as simple as water hammering where you get a flood of water which catches up with the fast moving vapour and that bangs around the pipework.”
Another approach is to model the performance of the plant in terms of it was originally designed to do.
“Heat exchangers are a good example. You can look at that heat exchanger and gauge whether it is performing at the rate it used to be perform to and you can use that information to perform intelligent maintenance. You can also model the performance it has now and decide when it is acceptable to take that kit offline and do the maintenance on it.”
“We’ve created models of whole plants to assess the impact of retrofit, say for example in replacing a turbine with a new steam turbine ” and using our data to compare with the original equipment manufacturer to help the station see if what they are being supplied with will work.”
Sub-components feature large among the common aspects monitored by the consultancy with the impact of transience on valving and valve sizing a case in point.
“We look to justify valve sizes and locations to try to mitigate against dynamic impact like water hammering which a plant commonly wouldn’t experience until it started two shifting and this phenomena occurred.”
The FT recently painted a gloomy picture for new power plant development in Europe for the rest of this decade, and while Frazer-Nash serves both new plants and those coming to the end of their working life, the benefits of modernising existing kit, and ensuring it can cope with the new reality, are apparent.
“Talking to generators the margins between running the plant and generating profit is lower and lower all the time so this comes down to a need to only operate when its profitable, when there is a high demand. With the smaller combined cycle gas turbine plants that are fast start up we can look and plan a model for over a year and plan when it expects to operate under market demand. We can look to optimise when they should be operating.”
Paul Verrill of energy data specialists, EnAppsys, recently told PEi that quicker and more flexible power plants were the key to preventing UK power blackouts, putting that priority ahead of adding new capacity.
Wherever you stand on what needs to be prioritised it makes the need for intelligent monitoring all the more urgent.
“The three key words that are bandied around a lot are reliable available and flexible and that’s what the capacity market was designed to do. For the power plant owners the biggest disappointment for them was the bid price ” the strike price they thought they were going to have was quite a bit lower than they were originally expecting. Because that strike price was so low it didn’t spur the necessary adoption of more efficient combined cycle gas turbine plants.”
“With a lot of the dirtier plants coming to an end and there being a gap before nuclear comes online, within three or four years, something will have to give and we might see more smaller plants quicker to fill a short gap.”
“What we can do is intelligently inform maintenance schedules to get work to be done in the summer when there is lower impact on demand. We can also look at how to make the plant more flexible and available so we can get the quicker start-ups that they are maybe required to do through the contract they got in the capacity market for example.”
In conclusion Naylor points to the valuable monitoring that can be of benefit to operators attempting to convert their fossil power plants into biomass facilities.
“There are a couple of UK stations, which could use this type of modelling to look at the impact of burning different types of biomass. Depending on the fuel source you’ll get different calorific values and we could, for example, look to optimise the boiler to accept a broad range of fuel types.”
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