Refining System Optimization-TỐI ƯU HÓA HỆ THỒNG NGHIỀN SỢI MDF

REFINER SYSTEMS System Optimization Optimizing a refining system will not only help to reduce operational costs but will also produce a higher quality Fiber more consistently Key areas to focus on are: •Steam consumption •Steam pressure stability •Refiner motor load •Motor load stability •Blowline and blow valve size REFINER SYSTEMS System Optimization cont Steam consumption Most modern MDF systems operate with a fiber to steam Ratio ranging from 3kg of fiber per kg of steam (3:1) To 5kg of fiber per kg of steam (5:1) As a general rule, a properly run system should consume steam within this range REFINER SYSTEMS System Optimization cont Steam Pressure Stability The stability of the steam pressure is critical to produce quality fiber If steam pressure fluctuates, the motor load of the plug screw and the refiner will be affected This can cause poor fiber quality and increased motor loads to compensate Steam pressure should be controlled within +/- bar ( +/- 1.5 psi ) REFINER SYSTEMS System Optimization cont Refiner Motor load Reducing refiner power consumption is an area that mills are constantly focused on The main factors related to energy consumption at a given throughput rate are: •Wood species and furnish type •Fiber quality demands •Refiner plate design •Steam tube pressure REFINER SYSTEMS System Optimization cont Motor load Stability Motor load stability is critical for the production of quality MDF If the refiner motor load flucuates, the refiner can not maintain a constant plate gap This can cause excessive fines to be generated as well as an increase in shive content Motor load swings should be no more than +/- 5% of the total applied load Which means, if you are applying 2000 kW of power, the load should be maintained between 1900-2100 kW REFINER SYSTEMS System Optimization cont Blowline and Blow valve sizing Blow valves have an effective operating range between 20% - 80% open The remainder of the adjustment has almost no affect on the system If a blow valve is constantly above 80% open, the refining system is not operating in a controlled mode and may require a larger diameter blowline and valve to operate within a controlled range Factors that affect blow valve position are: •Throughput •Steam pressure and volume •Specific energy •Blowline length and path REFINER SYSTEMS Fiber Characteristics that determine quality • Fiber Length • Fines Content • Shive Content • Fiber Color • Bark Content REFINER SYSTEMS Fiber Length Ideally, a short well developed fiber produces the best MDF fiber where routing deep into the board is required Smooth surface boards also requires short and uniformed fibers However, thin board may require a longer fiber length to achieve adequate physical board strength A well developed fiber allows for optimum resin coating and bonding which improves board strength and density REFINER SYSTEMS Fines A certain amount of Fines are generated during the refining process Though a percentage of fines in the board can help board finish, too high of a content contributes no bonding properties or strength to the board Fines are generated with: * Low moisture content in furnish * Low steam tube retention time * High refining energy * Too restrictive refiner plate design REFINER SYSTEMS Shive Content Shive content in MDF will vary depending on your individual market demands Usually, shive content is controlled between 2% and 15% Factors effecting shive content are: • • • • Amount of energy applied Throughput Refiner plate design Furnish geometry and uniformity REFINER SYSTEMS Fiber Color Fiber color may or may not be an issue for your mill depending on what your market demands are Factors effecting fiber color are: • High retention time in steam tube • Fiber burning during refining • Non wood contaminants ( plastics, bark, natural rosins ) • Lignin extraction in steam tube • Furnish type and species Typical MDF Process Requirements • • • • Minimize energy consumption Low raw material cost Board strength with Resin usage Consistent board surface appearance REFINER SYSTEMS Refining System Tools • • • • Preheating time & temperature Refiner inlet & outlet pressures Dilution water addition Plate pattern & diameter REFINER SYSTEMS Effect of Plate Gap • Plate gap determines the relationship between energy applied & fiber quality Goal : low shive content with minimum energy application How to achieve : small plate gap REFINER SYSTEMS The Effect of Plate Gap cont Decreasing refiner plate gap will produce: •Higher motor loads and SEC •Reduction in shive content •Potential increase in fine generation •Increased dwell time between plates •Potential decrease in throughput and steam handling REFINER SYSTEMS The Effect of Plate Gap cont Increasing refiner plate gap will produce: •lower motor loads and SEC •increase in shive content and coarse fiber •Reduced fines generation •Decreased dwell time between plates •More efficient steam handling and higher through put REFINER SYSTEMS Refiner Inlet & Outlet Press • Positive casing pressure – Retards fiber flow through plates • Increases specific energy at a given plate gap • Increases back flowing steam – Reduced steam consumption – Limit - feeding problems and refiner load variation • Negative casing pressure – Speeds fiber flow through plates • Reduces specific energy at a given plate gap – Limit - fiber becomes too coarse • Increases steam to blow line – Benefit - fiber transports to dryer easier – Limit - increases moisture to dryer and steam usage REFINER SYSTEMS ...REFINER SYSTEMS System Optimization cont Steam consumption Most modern MDF systems operate with a fiber to steam Ratio ranging from 3kg of... appearance REFINER SYSTEMS Refining System Tools • • • • Preheating time & temperature Refiner inlet & outlet pressures Dilution water addition Plate pattern & diameter REFINER SYSTEMS Effect of... plate design •Steam tube pressure REFINER SYSTEMS System Optimization cont Motor load Stability Motor load stability is critical for the production of quality MDF If the refiner motor load flucuates,