Products

COAL TO BIOMASS MILL CONVERSIONS USING STATIC CLASSIFICATION



 Coal Milling Projects
Coal Milling Projects is a South African based company with 20 years’ experience in the Power industry primarily on coal fired Power Plants and more recently Biomass firing.Star CCM+
Coal Milling Projects uses Star CCM+ Computational Fluid Dynamics Software exclusively for all CFD modelling and has an extensive database of empirical mil operating data for model calibration and practical evaluation.Southwestern Corporation
CMP is a global partner of the Southwestern Corporation in the USA and reciprocally shares and develops Patented technology for use on Coal or Biomass Mills.Babcock e-Type Mill
The Drax UK 10E mill has been successfully converted using patented Rotating Throat technology and sophisticated CFD modelling.  The Static Classifier has been completely modified to reduce recirculation and pressure drop build up and to match the Rotating throat flow characteristics.The requirement fort particle size and required throughput was achieved.

Burner Isolators isolate the mill and its associated components from the running boiler and possible flashback from the boiler through the pulverised fuel pipes. For this reason, Burner Isolators are situated as close as possible to the boiler.

The Isolators are closed during maintenance on the mill internals and primary air and pulverised fuel systems. Orifices are often required in pulverised fuel pipes to offset differences in total pipe length and balance pressure between the fuel pipes on each mill. The Burner Isolators are designed so that the housing will also accommodate an orifice plate.

Southwestern Burner Isolators comply with National Fire Prevention Association (NFPA) code requirements, being designed for 350 kPa service and tested at 1 400 kPa.

 

Coal Milling Projects (CMP) have the capability to design, fabricate and install transfer chutes and hoppers required for the handling of bulk materials.  CMP was awarded the design, manufacture and installation of coal transfer chutes at both Arnot and Hendrina Power Stations.  Subsequent to these projects CMP together with Aerotherm and Bulk Solids Flow SA developed the in-house capability to design chutes using proven coal specification analysis and Discrete Element Modeling (DEM) verification.  This was put to use on the Kriel coal transfer chute design due for installation in 2012-2013. The Coal transfer chutes at Arnot where designed by CMP and have been operating successfully with the full range of coal conveyed including wet coal.

A full design of Coal Transfer systems is performed from material testing to 3D modeling from flow calculations and discrete element verification to the complete development of manufacturing drawings. This has been performed for Arnot, Hendrina and Kriel Power Stations coal handling plants.

Coal mill desander

MILLING PLANT SPECIALISTS FOR POOR COAL CONDITIONS
Remove sand from coal during the milling process.

 

The Desander Patented Technology is used to extract heavy minerals out of the mill during the milling process. This has a major impact on the wear rate of the grinding elements and the down stream effects of boiler tube and duct erosion.

PROPERTIES OF COAL

Origins of high ash coal
High ash coals were formed primarily in the Southern Hemisphere as the supercontinent separated and glacial action contaminated the existing coal deposits. The Southern Hemisphere continents and India share very similar coal properties.

Origins of high ash coal
Coal consists of Pure Coal, Minerals and Moisture which can be broken down into sub categories. The carbon analysis determines the combustion characteristics. The Mineral matter determines the grindability and the moisture determines the mill design for drying purposes. The Mineral component is the area targeted by the Desander for heavy particle extraction.

Extraction analysis
The heavy material extracted consists mainly of Quartz, Pyrite with a measure of Carbon to determine the extraction efficiency. Too little carbon extracted and the process is allowing sand to return to the grinding zone, too much carbon extracted results in carbon wastage.

 

Coal Milling Projects (CMP) are the agents for Merrick Industries a leader in the design manufacture an installation of slack belt type gravimetric belt feeders. CMP was awarded a contract to install 27 gravimetric belt feeder at Komati Power Station. In addition to this existing belt feeders can be converted to gravimetric using Merrick’s load cell technologies.

Other auxiliary products used in conjunction with coal feed systems such as blocked chute detectors, coal feed gates, diamond back hopper designs and feeder drive retrofits can be designed to your plant requirements.

 

The main purposes of the Southwestern High Performance Static Classifiers (HPSCs) are to improve coal fineness control and increase maximum mill throughput.

The HPSC design incorporates the following features to achieve these improvements: Mill Top Extension – to increase the volume of the mill housing and allow for installation of the cyclone separator Pre-swirl Vanes – to control airflow in the upper mill housing, thus increasing the efficiency of the classifier blades Intermediate Deflector Liner – to redirect the upwardly moving coal and initiate intermediate classification Enhanced Classifier Blades – larger than standard blades and contoured to fit the mill housing.

Cyclone Separator – to increase the classifier volume and to segregate larger coal particles from the coal stream.

Multiple Outlet Turret – to improve distribution to the pulverised fuel pipework.

Slew Ring Assembly – to allow on-load classifier vane changes from a single actuator.

Installations at Arnot, Camden and Matimba Power Stations have resulted in significant increases in mill throughput with improved fineness. At Matimba Power Station, the fineness improvement was 15% with an average throughput improvement of almost 21%. At Camden Power Station the maximum throughput has been increased to almost 30 tons per hour (tph), from a design rating of 22 tph. A trial installation has been done on the 12.9E mills at Matla Power Station with a 17% throughput improvement.

CMP has designed a range of Isolating Gates to meet specific Customer requirements. The Isolation Gate slide operates outside of the coal stream, thus avoiding contamination of the slide area and restrictions common in other designs used in these applications. These gates are designed taking into account coal flow and pressure head requirements. The gates are FEA & flow modeled to ensure continuous coal flow and durability and can either be manual or actuated depending on design requirements.
CMP has supplied over 200 Southwestern Rotating Throat conversion kits to various Eskom Power Stations and other mill operators in South Africa. The Rotating Throat conversion employs the following design principles:
  • Reduction in air velocity through the throat area
  • More uniform air distribution in the grinding area
These effects are achieved by increasing the area of the throat opening, whilst at the same time attaching the enlarged throat, in the form of fabricated steel segments, to the rotating portion of the mill. The following operational characteristics are apparent after modification:
  • Reduction in mill differential pressure
  • Reduction in PA inlet pressure
  • Reduced wear in the throat area
  • More efficient mill operation, typified by an increase in reject rate and a reduction in mill and fan power
  • Throat velocity can be changed by adding or removing restriction rings to alter the throat area
Rotating Throat conversion kits are made up of rotating and stationary sections. The rotating sections are fitted to drilled and tapped holes in the mill table, whilst the stationary sections are welded to existing wall liners in the mill body. CMP have of late developed improved high performance rotating throats designated as our version 3 & 4 designs which substantially improve mill performance over the original designs.