ALIGAS

ALIGAS is a collaborative project lead by the Biomass department at CENER (National Centre for Renewable Energies). And the AIN (Navarre Industrial Association) is participating as a member, specifically their Measurement, Control and Communications department.

This R&D project reached its third and last year of execution and, after finishing the planned activities, the results achieved were assessed very positively. The final solution adopted was to use three specific controllers that are parametrised according to the material being fed (straw, wood chips and pellets), or density in the HMI/SCADA. With those three controllers, it was possible to make the biomass and heterogeneous waste feed to the reactor more stable, precise and reliable than with the current control system.

A controller is a device that makes it possible to control a system using an algorithm or set of instructions so it reaches the desire output state. Automated control plays a very important role in manufacturing, industrial, chemical, naval, aeronautic, robotic, economic and biological processes. Controllers were invented to simplify the tasks of plant operators and have better controls over operations. Some of the most common uses are: temperature controls (for example in heaters and refrigerators), level controls (for example in tanks of liquids like water, milk, mixtures, crude oil, etc.), pressure controls (to maintain a specific pressure in tanks, tubes, containers, etc.), and flow controls (to maintain a flow inside a line or pipe). In the specific case of this project, improvements in the flow control of solid feeding to be implemented in biomass boilers and other value producing processes were developed.

While doing this project, a series of tests with different kinds of biomass were done, both in the torrefaction pilot plant and gasification pilot plant at the “Biorefinery and Bioenergy Centre” (BIO2C) that CENER has in Aoiz. With the tests done at both plants the problems of the current controller of the feed system were identified, the suitability of the flow calculation was analysed, and it was verified that the system behaves in a very different way depending on the density of the material, especially depending on the kind of biomass or waste fed (straw, wood chips or pellets).

After the current feed systems were identified in both open loop and closed loop, the next job was to calculate new, more efficient controllers for those systems. PID and MPC controllers (model predictive controllers) were developed. Reducing the maximum overflow was more important than actuation speed in the controller design. That is because it is not absolutely necessary for the system to act very fast, because its dynamic is very slow, but especially because fast increases in the flow of the material fed can cause sudden increases in the temperature of the reactor, which can cause stoppages in plants.

The new controllers or control algorithms were verified primarily through simulation, but they were subsequently programmed and integrated into the CENER pilot plants. Lastly, they were validated with in plant tests with different biomass materials, resulting in a large improvement in its behaviour, because the initial peaks in the open and closed loop control steps were prevented, the variability of the flow could be reduced with the filters implemented, and the maximum pending flow could be limited to avoid problems in the plant reactor.

The results obtained with this project have an important application in bringing energy value with biomass and heterogeneous waste, because it solves a real operating problem many industrial plants have when feeding those fuels. With the solution chosen, greater operational stability in controlling the feed flow of biomass and heterogeneous waste is achieved through parametrising the property that defines its behaviour, which in this case is density.