This master's thesis describes a system for the automated nitrogen oxide (NOx) emissions reduction during the production of clinker, the main raw material of cement. Air emissions upper limit values are determined by the environmental permit [1], which follows law demands and concepts of the Best Available Techniques (BAT) [2, 3, 4]. Demands for upper limit values of air emissions are getting lower along with the development of these technologies. Given the changed limit value for nitrogen oxides [3] we decided to utilise one of the best existing technologies (BAT 20 for cement industry) [2], the process of selective non-catalytic reduction (SNCR), which reduces the amount of NOx emitted from the rotary furnace by using urea (CH4N2O). The systems for preparing the solution and injecting it into the calciner are designed to operate automatically, without additional burden to the operator. The process is divided into two parts; the preparation of the solution according to recipe and the injection of the urea into the calcinator as the process demands.
To automate the NOx reduction process, we updated the existing Siemens S7-416-2DP controller and its iFix 5.8 control system. Two independent cabinets with corresponding input/output modules were added to the system and connected to the existing profibus network. We decided to utilise the existing SCADA (Supervisory Control And Data Acquisition) control system and the iFix 5.8 software. The SCADA system allows for remote supervision and operation of connected devices from the command desk. In congruence, the iFix 5.8 software enables a link to the controller and the drawing of a graphic representation for control and supervision of the process, as well as storage and analysis of values accumulated from the devices. The aim of the thesis was to implement the automatically controlled system on the control computer.
First, the controller driver was installed on a virtual database server. Using the TCP/IP protocol, the controller was connected to the server, which was linked through the ethernet network to physical computers with graphic display. The virtual server facilitates data storage and transfer to other servers. The servers used are the SCADA terminal for data archiving with the Proficy Historian 7.0 software, as it allows for data insight and analysis from multiple users; a database server on which data is refreshed; and the SQL (Structured Query Language) server, which connects the aforementioned servers and records all events across all servers and the computers connected to it. The physical computers intended for management must have all the aforementioned server connections configured, or the data will not be displayed. When the connection between the servers was established, we began to create the graphic display of the process of urea injection. Usually, the process is displayed like in an electrical plan and as the actual devices are positioned. To facilitate image realisation, we use the iFix tool. Designer tool Workspace is utilised to construct the graphic display with animation, the VBA (Visual Basic for Application) programming language enables the graphic display to be used as a command for alterations in either the controller or the SCADA and Database Manager, which operate with the database connected to the virtual server. The system had to be set up twice, since it was tested on the test server, and was only moved to the production server due to testing during operating production.
As expected, the NOX emissions to the air have been reduced as expected by means of SNCR so that values under 500 mg/Nm3 were guaranteed. Automatic system works impeccably. The operators do not have problems with controlling and managing, while the system is also clear and useful to supervisors. We strive to optimise this system and reduce NOx emissions by initiating improvements, that is why we will regulate urea flow and install an additional spraying nozzle.
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