Visualization with PLC functionality in a biogas plant

The conversion of biomass into electrical energy is widely-used in Germany. In addition to the construction of new plants the need to upgrade existing plants is increasing. The main focus is on easy operation, optimization of process flow and flexible access to system parameters and user data. With the use of C6 HMI-LC it is possible to expand the system with a subordinate control in combination with a comfortable visualization and directly connected to it a remote maintenance.

1. Application Description:

In a fermenter with gas storage bacteria are grown to produce biogas. Ideal conditions for this process are provided by pressure and temperature control as well as the constantly monitored supply of raw materials. A screw conveyor takes over the input of solids and a pump station feeds the liquids into the fermenter. The remaining residual product (digestate) is pumped into an interim storage. To ensure that nothing clumps together and to achieve a better mixing of the material in the fermenter, all tanks are equipped with agitators. The produced biogas is filtered and supplied to the CHP (combined heat and power plant), where a motor / generator set generates the electrical energy. The thermal energy that develops during the process is used in parts by the user and fed into a heating system

The entire CHP is managed by a superior control. Subordinated to it, the monitoring and control of the gas-generating process through controlled feeding and removal of solids and liquids together with the complete user guide is reproduced in KEB C6 HMI-LC.

The feed screw and the agitator of the fermenter are controlled by the frequency inverter. Additional agitators, pumps and valves are directly triggered via contactors and relays.

2. Employed KEB products

2.1 Control:

A C6 HMI-LC with 15.6-inch widescreen is employed as control. It includes an integrated PLC functionality for visualization. With EtherCAT-bus C6 remote I/Os are connected, which detect digital as well as analog inputs and switch outputs.

The control manages the manual operation, i.e. all motors can be switched on and off manually. In automatic mode the preset feeding and removal cycles of the biomass are executed. In the user menu the operator simply adjusts the time intervals and the duration of the actions.

The set-point speeds of the agitator in the fermenter and the feed screw for the supply of solids are given analog to the frequency inverter. Starting commands to frequency inverter, contacts and relays are given digitally.

The measured pressure and temperature values are evaluated by the control and appropriate actions, such as opening the valves to discharge the biogas, are carried out.

The interface between CHP control and the C6 HMI-LC is a very simple design with analog and digital inputs and outputs for exchanging set-point values and status signals.

2.2. Visualization:

2.3. Remote Maintenance

Access to the plant data via internet at any time is provided by the installed C6 router, where recorded data is stored and transmitted, if required. In addition, the system offers the possibility to either diagnose or upgrade the project in case of service. The internet connection is established via mobile telephony (UMTS) and is therefore independent of the customer’s network.