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Comment: Re:Pointing out the stark, bleeding obvious... (Score 1) 247

The grid technical paper specifically listed multiple different sizes of OCGT and their ramp rates, so I presume that they do matter.

However, checking the specification sheet for a state of the art large turbine (GE 7HA), the ramp rate is 40 MW/min for the 275 MW model, with a manufacturer claimed startup-signal to full load time of 10 minutes.

By contrast, checking the spec sheet for the same manufacturer's small turbine, they claim that the turbine can ramp to 20 MW (45%) from idle within 5 seconds. I could well imagine that such a turbine could start, synchronize and ramp to full power within 1-2 minutes.

Comment: Re:Pointing out the stark, bleeding obvious... (Score 1) 247

My figures were taken from a 2012 report by my local grid operator, based upon operational data supplied by the power plant operators.

The figures are conservative, but they are based upon the figures declared by the plant operators, based upon existing plant, but some consideration has been given to new-build plant. I accept that I omitted the issue of ramp "elbow" for CCGT, but that was for simplification.

As to the ramp rate of OCGT, it varies with size. Aero-derivative OCGT (20-60 MW range) can certainly come to full power within 3 minutes. Large frame OCGT (200 MW range) are slower. Even a state-of-the-art turbine needs at least 10 minutes to come to full power from cold shutdown. Most existing plant is slower.

Comment: Re:Pointing out the stark, bleeding obvious... (Score 1) 247

Nuclear plants are modestly controllable, but it is rarely done, because the cost savings of ramping down are negligible, so typically nuclear plants only ramp down for operational reasons, or grid acceptance reasons. In countries with large amounts of both nuclear and renewable power, nuclear plants operate in a load-following mode, ramping up and down with demand/renewable supply.Old nuclear plant normally offer ramp rates of 2.5% of nameplate rating per minute, with more modern plants offering 5% or greater. There can be some issues with ramping older plants because of temperature changes in the reactor which can contribute to fatigue and limit the reactor life time. Modern plants are designed for isothermal ramping to prevent reactor thermal fatigue from load following operations.

Large coal plants typically can achieve approximately 2% per minute, with the more modern coal gasification combine cycle plants achieving approximately 3%. The big problem with coal plants is start up time after a shut down. A hot start (48 hours) can incur an 8-12 hour delay.

Most existing combined cycle gas turbines can ramp at approximately 3% of rating per minute, with a 60 minute start up delay from warm, or 3 hours from cold. Modern (new build) combined cycle gas turbines can ramp at approximately 5% of rating per minute (when hot), or approximately 1% per hour from cold start with a 15 minute start delay.

Open cycle gas turbines can ramp at approximately 10% of rating per minute, with a cold start delay of approximately 10 minutes.

The big advantage of OCGT is that they can start from cold with minimal notice, so for short-term peaking, they are excellent.

Modern CCGT has most of the benefits of OCGT, but a very much higher capital cost - so there needs to be adequate baseload demand to make the economic case for CCGT, even though efficiencies can be considerably greater with CCGT (62% for a state-of-the-art CCGT, compared with 38% for state-of-the-art OCGT).

In California, utilities are building OCGT like crazy, because it's the cheapest way to provide rapid start standby capacity when the Spring/Autumn Sun starts to go down, just as demand starts to peak.

Comment: Re:Can you get this in concentrated form? (Score 2) 190

by ChumpusRex2003 (#49249341) Attached to: Powdered Alcohol Approved By Feds, Banned By States
It is possible to sorb ethanol into a dextrin. The problem is that the volume/mass of sorbent is much larger than the amount of alcohol that can be bound.

So, if you want to bind 10 ml of ethanol (approximately 1 shot), then you may need 100 grams of powder. Which makes the product of limited value.

If, however, you want something iso-intoxicating to 10 ml of ethanol, you can reasonably safely do that with about 500 ul of 2-methyl, 2-butanol, which could be sorbed in 5 grams of powder. The latter is a practical product which meets the description of "palcohol"

Comment: Can you get this in concentrated form? (Score 2) 190

by ChumpusRex2003 (#49246299) Attached to: Powdered Alcohol Approved By Feds, Banned By States
Never mind the powdered form, what about getting the liquid in concentrated form?

"Palcohol" is not ethanol, but the highly intoxicating 2-methyl, 2-butanol, which is about 30x as potent at causing intoxication as ethanol. Despite being termed one of the "toxic alcohols", it probably has lower chronic toxicity than ethanol, as being a tertiary alcohol, it cannot be oxidised to toxic aldehydes/ketones.

Comment: Re:What about military satellites (Score 1) 178

by ChumpusRex2003 (#49215059) Attached to: MH370 Beacon Battery May Have Been Expired
Not quite correct. Galileo (when it is eventually commissioned) will specifically have the ability to detect the signal from 406 MHz from emergency locator beacons.

Because existing beacons use signals not designed for time of arrival detection, location would still rely on Doppler processing techniques, but location to within 1 mile or so should be achievable with this system. There are plans to change the modulation of emergency locator beacons to permit time-of-arrival localisation with 10 meter precision.

Comment: Re:Are we sure it went south? (Score 3, Informative) 208

There are several sources of Doppler shift and compensation. There is Doppler shift between aircraft and satellite, and between satellite and ground station. The ground station automatically compensates for all the Doppler shift between GS and satellite.

The Doppler shift between aircraft and satellite is partially compensated by tracking the Doppler shift in transmissions from the satellite to the aircraft. Without compensation by the aircraft, Doppler shift would be in the region of 300-400 Hz, which exceeds the bandwidth of the channel allocation. The compensation is subject to local oscillator error in the aircraft transceiver, hence individual aircraft will apply the compensation slightly differently.

Although the degree of compensation varies between aircraft to aircraft, it could be fitted with a standard linear regression. This method was apparently verified by Inmarsat on several other aircraft with similar transceivers, and was calibrated based upon transmissions with known locations/velocities.

Comment: Re:I have said it before (Score 1) 384

by ChumpusRex2003 (#49191143) Attached to: French Nuclear Industry In Turmoil As Manufacturer Buckles
Indeed, most of the issues with the EPR could have been predicted and prevented - it has been a clear example of inept project management. The major problems have been:
  • Out of spec concrete: Nuclear grade concrete needs strict porosity control, and very large seamless pours. Conventional concrete formulations and QA techniques (slumping) are not feasible, and advanced formulations blended to strict proportions are needed. The problem is that the contractors they employed to do the concreting lied about their ability to make nuclear grade concrete. When the regulator inspected the site in Finland, they found that the concrete contractors were blending the aggregates and cement without taking into consideration the water adsorbed onto damp materials. As a result the concrete did not meet the porosity specification. The foundation slab had to be relaid.
  • Out of spec welding: This was further compounded by the fact that many of the required welds were first-of-a-kind, requiring welding of unique dissimilar metals at unprecedented scales in very difficult configurations, requiring the development of new welding equipment as it became clear during dummy runs, that existing equipment could not achieve the quality required
  • Problems with scale: The sheer size of the EPR and volume of concrete and steel for the containment made it difficult to source enough workers of any skill. There were frequent communication problems due to language barriers, and it was difficult to ensure that all staff were kept aware of issues. For example: Areva were unable to source enough welders locally. Welders from as far away as Bulgaria were brought in. However, due to language difficulties and inexperience with the QA required, many welds were not made to adequate quality and had to be remade.
  • Overly aggressive construction schedule: The planned construction would have been the fastest construction of a nuclear plant ever, quite a bold claim, considering that hte EPR is also the most complex ever builtstarted.
  • Insufficient skilled staff: Construction started before design was complete. In particular, control systems had not completed design and verification. The prime contractor also had insufficient architects and engineers to ensure that all designs had been completed to the level of detail required for construction.
  • Failure to validate the supply chain: Construction started before the designers had adequately assessed the global supply chain for parts. There were numerous delays due to excessive lead times for parts which had not been planned for, particularly as many part manufacturers had wound down their facilities due to the death of nuclear plant construction in Europe.

Similar issues, but to a much smaller extent have also cropped up in France on their EPR construction. They've had problems with poor quality welding too, as well as difficulty finding enough competent staff.

Comment: Re: What a wonderful name! (Score 1) 267

You mean 200%. Electricity costs in the UK are $0.06/kWh in bulk. Offshore wind has a breakeven price of $0.25/kWh. Things may change in time, and I wouldn't suggest withdrawal of subsidies until we see the potentials and unavoidable drawbacks of the technology. However, to illustrate the point, the UK government recently announced a plan to cut the offshore wind guaranteed purchase price to $0.24/kWh and suddenly a whole bunch of investors threatened to pull out of projects, so the govt backtracked.

Comment: Re:Cape Wind Will Die (Score 1) 267

A major reason Germany can cope with large amounts of renewables, are because its grid is tightly tied to numerous neighbouring countries. Effectively, the whole of continental Western Europe is tightly interconnected and synchronised.

This allows Germany to use imports/exports to help absorb fluctuations in wind supply outturn. Germany have also been shutting down slow responsing nuclear plants and replacing them with coal and gas turbine plants which are faster to respond.

However, the UK has had significant problems with grid stability after the establishment of a large amount of wind energy. National grid have already increased the maximum allowable "rate of change of frequency" (ROCOF) to 1 Hz/s, because their previous operational limit of 0.1 Hz/s was being continually exceeded due to wind variability. For interconnected systems which depend on ROCOF to detect grid failure (e.g. small scale generation - combined heat power schemes, rooftop solar PV, small scale wind), the previous operational limit was being exceeded frequently enough to result in various "chain reaction" type events. For example, a thermal power plant trips out, causing frequency to fall at a significant but not critical rate - at the same time a random variation in wind output results in a temporary loss of output. Together, this is sufficient to trigger ROCOF protection on embedded generators, causing them to trip off, suddenly withdrawing supply to a grid which already has an excess of demand. Some of these events have been severe enough to trigger emergency load shedding with up to 50k homes disconnected due to low frequency.

Comment: Re:What a wonderful name! (Score 1) 267

I was wondering how this was going to cut power prices. In the UK, which is now the world leader in offshore wind, the levellized cost of off-shore wind energy is approximately $0.25/kWh at the onshore cable termination.

Obviously, this is completely non-viable for a large grid without subsidies (in the UK, these are approximately $0.19/kWh), but for a small grid dependent on expensively imported diesel, this can be a reasonable idea.

Comment: Re:It's worse than just 0.5 GB of slow memory (Score 1) 161

by ChumpusRex2003 (#49105085) Attached to: Nvidia Faces Suit Over GTX970 Performance Claims
It has 7/8 of the processor. In traditional GPU designs, this would mean that only 7/8 of the RAM is addressable and that the RAM data bus is only 7/8 as wide - as parallel modules of both stream processor, L2 cache and memory controller get disabled.

The 1st 3.5 GB operates on the 7/8 wide bus (224 bits); this is the same as on any other reduced core count card. However, nvidia added a new "bypass" bus inside the GPU permit 2 memory controllers to be driven by a single L2 cache module. This avoids the need to reduced addressable RAM in the event of a L2 cache module being disabled. This last memory controller without a dedicated L2 cache module then accesses the top 0.5 GB of RAM via a 1/8 wide (32 bit) bus.

Comment: Re:A precaution when done ahead of time. (Score 1) 311

by ChumpusRex2003 (#49068587) Attached to: Nuclear Plant Taken Down In Anticipation of Snowstorm
The key point is to allow the reactor to cool for 24 hours or so in a maximally controlled environment - grid power, with backup diesel generators and full tanks for fuel. Once you're through the first 24 hours, the thermal load of decay heat is almost an order of magnitude lower, and much easier to handle.

It is also undesirable to expose the plant to grid transients. Short circuits on the grid, can cause severe mechanical disturbances to the alternator and turbomachinery. In a nuke plant, the LP turbines are typically very large, low speed machines with huge blades. These are susceptible to shock loadings due to their high moment of inertia. In fact, in nuke plant turbines, grid transients are one of the most important factors in determining fatigue life of the turbine assembly.

More over, there is a degree of thermo-hydraulic coupling between the turbine and reactor (or at least the steam generators) - these pressure and heat transients are also a contributor to fatigue life of the primary coolant circuit.

Comment: Re:A precaution when done ahead of time. (Score 1, Informative) 311

by ChumpusRex2003 (#49068511) Attached to: Nuclear Plant Taken Down In Anticipation of Snowstorm
That's not quite correct. There was no some damage to the emergency cooling systems, but it wasn't catastrophic.

At unit 1, the emergency isolation (condenser) cooling system (UPS powered) were manually turned off about 20-30 minutes after the earthquake, because they didn't want to "cold shock" the reactor, and switched instead to alternate methods of cooling (which required AC power). In the confusion that followed loss of AC power, they relied on staff to run outside and check the emergency cooling vents for steam. Staff were not familiar with the volume of steam which should flow from the isolation cooling system (should completely engulf the plant in thick cloud) and reported "faint steam" which was presumed to be due to operation of the isolation cooling system - but was, in fact, residual heat in the vent stacks, as they cooled following shutdown of the isolation condensers. Unit 1 likely suffered total core meltdown within 3-4 hours of the earthquake.

At plants 2 and 3, the emergency cooling system failed after the UPS systems powering the control systems depleted their batteries - a period of about 9 hours after the earthquake. Partial meltdown likely occurred within a few hours of core cooling loss. The extent of core damage is much lower than occurred in unit 1 because the first few hours are when decay heat is highest, and therefore severity of meltdown drops dramatically once through this period.

Fire pumps were brought in to inject water into the reactors at units 2 and 3. In this case, the water pooled in a tank and never reached the reactor. This was not due to a valve fault. The plan to inject water using fire pumps was an ad hoc plan, and the assumption was that the tank was connected to the injection line via a "positive displacement" pump (which would act as an obstruction to flow when unpowered), in fact, the pump was an impeller pump, through which the water could flow with ease. Even if this had worked, this was too late anyway, meltdown would have been near complete by the time the pumps were brought on site, and connections made.

The main lessons learned were: Don't turn off safety systems during an emergency Make sure staff are able to recognise the correct operation of safety systems Ensure that plans for the emergency provision of cooling water are pre-prepared, validated and well rehearsed. Ensure that emergency portable pumps are available near (but not too near) to site, and that their performance has been validated as acceptable Ensure adequate redundancy of hydrogen-oxygen catalytic recombiners Don't forget about the fuel pools.

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