In last years, combined cycle power plants are being more used, since it has been an increase in its performance with respect to the conventional plants.
Due to the rapid growth of the energy sector and the electricity demand in the world, a lot of money is being invested in the development of new production techniques that support renewable energy and increase its performance against conventional methods.
A thermosolar plant consists in a solar-hybrid Brayton cycle that uses concentrated solar power to heat up pressurised air driving a gas turbine.
This is the process that follows a solar-hybrid Brayton plant to produce energy:
The objective of this project was to model and then optimize the physical processes that take place in this plant.
First, we needed to construct the data set. Here we used the leading developer of thermal engineering software, called Thermoflex, to collect historical data from all the variables into a single file. As always, the data was treated in order to fix faults and improve the quality.
We compared real data obtained from the plant to the one our team calculated using Thermoflex. The next table shows the data obtained from the images, ambient variables for a nominal summer day and the estimated fuel mass flow "Fuel Flow (T)" with its corresponding generated power values "P(T)" so we could compare it to the real ones obtained from thermosolar "(S)".
|Fuel flow (S)
|Fuel flow (T)(Kg/s)||Power (T)
As we can see, fuel values obtained with Thermoflex match with the image of the real data from thermosolar.
This are the different variables used in the data set:
The next step was to study the data and design the neural network. To do that, we applied different statistic methods. Studying the scatter charts, we could clearly see that the generated power increases linearly with the fuel flow mass. This is due to two things:
Then, we studied the correlations between the variables and between the variables and the target. In general, the target depends in many inputs simultaneosly, but it is interesting to look for linear dependecias among them. You can see the correlations in the following table:
|Generated power correlation|
|Air mass flow||0.152|
|Fuel mass flow||0.974|
A surrogate model is an engineering method used when an outcome of interest cannot be easily directly measured, so a model of the outcome is used instead. Most engineering or physics problems require experiments or simulations to evaluate the objective function and constraint functions as a function of control variables. In this case, the neural network represents our surrogate model.
A graphical representation of the network architecture is depicted in the next picture. It contains a scaling layer, a neural network and an unscaling layer. The yellow circles represent scaling neurons, the blue circles perceptron neurons and the red circles unscaling neurons.
After building the neural network, it is necessary to train it to obtain the best possible performance. In this case, we applied the quasi-Newton training method.
We can see that the final selection loss and the final loss are very similar. If these two values were different it would be producing overfitting during the training.
Once the predictive model has been trained, it is necessary to evaluate its predictive power on new data that it has not used before. This will determine how good is the model and determine wether the model is good enough to be moved into de production phase, the grey line would indicate a perfect fit.
Another testing method that we can perform is error data statistics. With it, you can measure the minimums, maximums, means and standard deviations of the errors between the neural network and the testing instances in the data set.
As we can see in the previous table, the mean percentage error is 0.54751% so we can conclude that the model has a good accuracy.
Once we have our predictive model tested, we are able to apply it in order to predict the generated power by thermosolar plant whenever we want depending on the input variables.
Optimal control is playing an increasingly important role in the design of modern systems. It has as its objective the maximization of the performance or the minimization of the costs of production.
Once we have modelled the physical system, in this case, the thermosolar plant production process, we are able to optimize it by minimizing the fuel consumption depending on other variables as irradiance, ambient temperature, ambient pressure, etc.
After defining that our physical constraint is going to be generated power at 4.6MW, we have determine which is the optmimal (minimum) fuel flow to keep the generated power at the defined level by oscillating the air flow, which is a control variable.
In the following graph you can observe the optimal fuel that the thermosolar plant should be using and the previous fuel which the plant was using.
By using our artificial intelligence technology, thermosolar plant managed to reduce fuel consumption, which made a big difference in economic savings and an improvement in plant performance.
|Daily fuel consumption (current)||17779 kg/day|
|Daily fuel consumption (optimal)||16668 kg/day|
|Yearly fuel savings||405763 kg/year|
|Fuel price||0.23 €/kg|
|Yearly money savings||94870 €/year|
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