GFMT Article: Saving energy in flour milling

Saving energy is a concern for most millers.  Today we take a look at how to reduce energy bills in flour milling in this article by Tuncay Lamci, General Manager, IMAS Integrated Machinery Systems, Turkey.

It was originally published GFMT Jan/Feb 2012.  Click here for the feature as it appears in the magazine or scroll down for just the text.

Energy saving in flour milling

by  Mr Tuncay Lamci, General Manager, Integrated Machinery Systems, Turkey

We all know that milling is an energy-intensive sector. Energy is the largest operating expense item after raw material costs. When lifetime costs are examined, we face amounts exceeding investment expenses.

For example, if we assume the investment cost of a flour mill of 200t/day capacity reaches five million TL (two million EUR) and its life time would be 20 years on average, then the annual depreciation cost will be 250,000TL (100,000 EUR). The annual energy cost of such a company will be around 500.000TL (200,000 EUR), twice the depreciation cost.

Departing from this fact, the fastest way to reduce production costs is to have focus on energy costs right after raw material cost.

It would be possible to get energy saving, through having maximum capacity usage in overall process by 5-10 percent, using high efficiency motors and total efficient maintenance by 2-5 percent, optimising air flow and avoiding leaks in conveying systems by 10-20 percent.

While the process uses 50 percent electric energy for milling and grinding, 30 percent is used for pneumatic conveying, 11 percent for mechanical conveying. For this reason, we will study energy savings under three main titles:

Methods of saving in motors

Conveying systems

Automatic control and energy management

Methods of saving in motors

Reducing the external load on motors, such as reducing air volume absorbed by the pneumatic system or preventing leaks from compressed air system would thereby reduce motor load, which must be considered as the first step for the saving.

The fact that efficient machines are chosen according to the targeted production tonnage and they are used at full capacity would reduce additional loads in motors and gears resulting from the system through bearing condition and oil check in line with manufacturer’s advice.

The choice with motor drive arrangement is of paramount importance.

For example, as the friction losses will be lesser with direct drive methods, they will work efficiently compared to chain or belt coupled systems. For bucket elevators, about 80 percent of the input power is directly attributable to the weight of material being conveyed with the remainder due friction, loading and discharge losses.

Chain transfer systems require regular oiling, whereas belt transfer requires regular check, setting and replacement.

The right choice of often used V-belts according to the pulley groove, synchronised replacement of multiple belts of the same brand, parallelism of the pulleys, tension of the belts are important parameters for the energy cost.

Reduction of motor losses, definition of size of motor being used in relation to the duty, choice of lowest motor for full load, high efficient motor choice rather than a standard one at replacement would therefore reduce losses and enhance saving opportunity.

A high efficiency motor of 90kW EFF1 type running 18 hours per day and 300 days per year at a plant, would yield 2500TL (1000 EUR) of energy saving in a year with actual energy costs.

Reducing the speed of motors means reduction in energy expenses.

For example, in pneumatic systems required air quantity for the transport of stock product varies with the ambient and seasonal conditions; setting motor speed by using variable speed drive would provide energy savings and would therefore return the investment cost.

Conveying systems

We will study conveying systems as four types: Mechanical conveying, negative pressure pneumatic conveying, positive pressure pneumatic conveying and dust collectors and aspiration.

Examples of mechanical conveying can be given as bucket elevators, screw and chain conveyors, in which some of the saving opportunities are use of products with proper bearings where the friction in these machines are at minimum, regular protective maintenance, product choice at right capacity.

Pneumatic conveying (negative pressure) in a system where ground stock product is carried, while volume of air moved changes, static pressure varies with the square of the speed, required power with the cube of speed.

In summary, when volume of moved air is reduced by 20 percent, fan speed is also reduced at the same ratio, whereas power consumption is down by 50 percent.

In pneumatic systems, removing vibration by mechanic balance, setting product and stock speed by a right system design and using minimum and wide angle elbow, optimising air volume to be absorbed by clacks, setting fan speed can be taken as first steps of a 10-20 percent saving in pneumatic system power.

Conveying with blowers (positive pressure) is an expensive conveying method that consumes same or more power than pneumatic conveying. Amount of power to be used changes according to, correct design of conveying line, periodic maintenance and cleaning of blowers, reduction of number of blowers by connecting lines required in the same area, dimensions and speed of air locks to be used, and distances between blades.

The most convenient method should be chosen among conveying systems.

For example, with a 10 tonne per hour capacity; while a mechanic system consumes 0.8kW of power for 20m vertical conveying, this consumption, which is 4.7kW in pneumatic conveying, reaches 5.0kW in blower conveying.

In aspiration system, by correct dimensioning, getting required airflow speed, preventing loss and leaks and by using manometer filters tracking filter cleanness and avoiding unnecessary energy expenses is possible.

Automatic control and energy management

In the aim of avoiding a general misunderstanding in the milling industry, it is needed to re-emphasise on the purpose of using automatic control in the system and its benefits.

Automation systems while they enhance system reliability through level measuring, flow measuring, scale equipments and failure warning switches and also thanks to the correct start and stop timing, they avoid unnecessary operations and make power saving independent of operator mistakes.

The capacity, which can be controllable through extraction scales, can be taken under control by extraction tracing and reporting through recording correct data.

In new generation mills where the number or the size of windows is reduced in order to prevent contamination, the choice with the lighting control and the energy efficient armature has gained importance.

To calculate milling capacity in the way not to run the plant at time zones with highest energy cost and if demand is available, to increase capacity, they must be carefully analysed since the latter will enable faster return of investment and if needed, be decided immediately without delay.

It should not be forgotten that the way to compete in global markets and succeed is through establishing energy efficient, effective and lifetime systems, by considering operating costs rather than investment costs.