Processing of brown coal

Processing of brown coal at RWE Power AG

The aim was the development of a SolidSim model for the coal processing and drying to ensure product quality in case of changes of feed composition or throughput. The simulation also simplifies and shortens the reaction on market demands.

The processing of brown coal to the different products as done by the RWE Power AG is shown in figure 1.

At the mines, the ROM lignite is loaded on to rail hopper cars and transferred to the ROM-lignite bunker. The lignite is pre-comminuted here in a precrushing station before being fed to the so-called wet plant, where two fractions of differing particle size are produced from the raw coal in screening and crushing circuits.
The coarse fraction is fed for combustion in the mine’s own on-site power plant, to generate process steam of 90 bar pressure. This steam is firstly used in turbines to generate electrical power, being expanded down to a residual pressure of 5 bar in the process.
The 5 bar steam is then used in the so-called dry plant for drying of the finer lignite fraction (“lignite fines”) produced in the “wet plant”. Drying down to water contents of between 12 and 20 wt.% is accomplished via condensation of the process steam in tube dryers. The dry lignite from the dry plant is then fed for further beneficiation (e.g. briquette and pulverized lignite production, or production of coke).
The cogeneration of heat and power used here permits achievement of high energy efficiency with the system described.

1.) Process unit model development

Brown coal is dried in rotary tube dryers. It was necessary to extend the SolidSim unit model library by a specific model for this kind of processing unit. The SolidSim unit model Software Development Kit was used to implement a new unit model based on a physical model and process specific know-how of RWE Power.

Figure 2: Rotary Tube Dryer

2.) SolidSim simulation model

Having developed the unit model for the rotary tube dryer the brown coal processing and drying process can be described in SolidSim. The simulation flowsheet consists of screens, mills, the rotary tube dryer and an electrostatic precipitator.

Figure 3: SolidSim flowsheet of the brown coal processing plant

3.) Model parameter adjustment

To achieve a good agreement of the simulation results with available measured process stream data some model parameters have been fitted using numerical methods. A data reconciliation step was performed beforehand in order to ensure fulfillment of mass balances also in the size classes.

Figure 4: Comparision of measured data and simulation results after parameter fitting

The trained model can now be used to obtain the material and energy balance of the whole process and to predict product properties.