Optimising plant components using flow simulations

1 Introduction

CFD (Computational Fluid Dynamics) makes it possible to predict system behaviour in detail far exceeding traditional and costly test set-ups. Heat transfer, pressure loss behaviour, velocity profiles, particle tracking velocimetry, flow phenomena and vaporisation processes are analysed using CFD simulation. CFD simulation programs have therefore developed into important tools for the analysis and optimisation of industrial plant components. 

Today, development processes have to be effective and efficient. Effective computer simulations offer an alternative to costly, conventional development processes, consisting of constructive development, prototype construction and experimental validation (in several cycles). CFD simulations are based on numerical fluid mechanics, the purpose of which is to solve fluid mechanics problems approximatively using numeric methods. The models used are based on Navier-Stokes-equations, Euler-equations and potential equations. At Intensiv-Filter, the optimisation of bag filters and plant components is  carried out through the networking of 3D CAD systems (Solid Works) with the in-house CFD program (CFX). Here, maximum synergies are achieved during the necessary process steps. After completion of the pre-processing steps, the actual flow calculation is processed overnight on high-capacity PCs.

At Intensiv-Filter, the typical component optimisation process using CFD is as follows:

­– 3D geometry generation (SolidWorks)

­– Pre-processing:

- Import of 3D geometry

- Generation of the solid that is flowed through, optimisation of sharp corners and edges

- Grid generation

- Input of operating parameters and material properties

 • Definition of flow

 • Definition of boundary conditions

– Solver flow calculation start

– Post-processing:

 • Evaluation and visual presentation of the results

The following demonstrates the integration of a flow simulation in process engineering and constructional design, based on existing dust removal installations.

2 Case study: Deuna Zement GmbH/Germany

The existing electrostatic precipitator was converted to a bag filter in order to remove dust from the rotary kiln at Deuna Zement GmbH. In addition to the further use of the existing ESP housing, a filter surface load of 60 m³/m²/h was achieved. To do this, unlike with conventional ESP upgrades, the raw gas plenum was fitted entirely with bags.

Due to spatial restrictions and the unfavourable raw gas inlet, an adverse flow into the dust collection chamber and an unfavourable upward flow into the bag packages were to be expected. The flow simulation was to provide information about the changes required in the inflow area.

The aim was to provide uniform incoming flow of the bags through a combination of a crossflow and a minimised (but not preventable) upward flow. For this, the structural design of various baffle plates and fin plates was varied (Fig. 1).

2.1 Results

The initial simulation results (Fig. 2) showed flow velocities of approx. 10m/s in the first dust collection hopper. Deflectors were then added to achieve a better flow distribution and to reduce the maximum velocity.

In a later step, the incoming flows of the filter elements were optimised to eliminate high speeds in the inlet area and dead zones, where turbulence and backstreaming had occurred. Damage to bags caused by abrasive dusts was prevented accordingly. A fin plate guidance system specially designed by ­Intensiv-Filter was used, resulting in the desired optimisation of the inflow behaviour.

In the final step, the uniform distribution of the volume flow below the bag packages was checked. A vastly reduced upwards flow circulated around the filter bags and the crossflow situation within the bag package was improved. The filter surface area is thus optimally utilised and the efficiency of the cleaning system supported in a better way (Fig. 3).

The flow optimisation resulted in:

– Uniform flow distribution around the filter bags and utilisation of the filter surface area through attaining the desired crossflow

– Uniform and low speeds in the entire raw gas plenum

– Minimisation of the upward flow between the bags

– Significant reduction of the filter cake resistance resulting in reduction of the differential pressure

– Reduction of operating costs

The uniformity of the bag inflow and low differential pressure in the filter have also been confirmed in practice.

3 Case study: Carpatcement, Bicaz plant, Romania

Intensiv-Filter converted the electrostatic precipitator into a bag filter and carried out the dust removal of the raw mills, clinker transport and the clinker dosing plant at the Bicaz cement plant in Romania. Intensiv-Filter was also additionally assigned with the optimisation of the existing evaporation cooler. The initial basis of which was a CFD analysis of the existing plant that had to be performed.

3.1 Results

Figures 4a and 5a illustrate the flow behaviour and the temperature profile prior to optimisation. The pipe bend upstream from the evaporation cooler causes an asymmetrical flow and temperature distribution in the evaporation zone, although liquid phase and dust content wall contact cannot be prevented.

As a result of the CFD-supported design optimisation, the evaporation cooler was directed through the centre of the upper cone by the use of deflectors (Fig. 4b and 5b). Behind the perforated plate manifold, a symmetrical flow without wall contact during the disperse phase was thus achieved in the cooler. This measure improves and optimises the evaporation of the sprayed water droplets, thus ensuring reliable and consistent direct operation for the downstream bag filter. Another advantage is the prevention of dust clogging in the evaporation cooler housing and the evaporation cooler dust discharge system.

On the whole, the measures derived from the flow simulation resulted in the improved energy efficiency of the entire installation and in a failure-free operation.

4 Conclusions

Today, efficient commercial CFD program packages enable fluid flow and thermal analysis and the resulting optimisation of plant components. The key to efficiently solving customer-specific tasks is the close interaction of the CFD program with the CAD system. Intensiv-Filter has therefore decided to perform CFD calculations in-house with its specially formed team of experts. In addition to the acceleration of process engineering and design project work during the planning and realisation of industrial dust removal installations, CFD also serves as a tool for fundamental developments. Through this, Intensiv-Filter can, from emission source to chimney, strengthen its core competence in the development of energy-efficient bag filters and filtration plants. 

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