Heat supplies the thermal energy required to properly form the fluted structure of the corrugating medium and to gelatinize the starch to bond the medium to the facings of the linerboard. Proper heat level and temperature is critical in determining machine speed and quality of bond. As the machine speed is increased or the grade of product increases, heat level demands rise. A slow machine or a machine having difficulty in running heavier grades or double wall are all symptoms of heat related problems.


Heat is made up of two components; temperature and quantity. The temperature component defines the rate of heat transfer with higher temperatures providing the ability to move a larger quantity of heat. For corrugating machines, surface temperatures should measure 350 to 360 F.

Heat quantity is measured in BTUs with one BTU being the amount of heat required to raise one pound of water one degree Fahrenheit. One pound of steam at 175 psig contains 847 BTUs of usable energy. A hot machine is then determined by the balance of the proper quantity of steam measured at the proper temperature.

Steam in a boiler operating at 175 psig contains 847 BTUs of energy at a temperature of 377 F. In theory a machine fed at 175 psig should have surface temperatures of 377 F. For heat to flow, a temperature difference is required. This difference in a machine is about 20 F which leads to our ideal range of 350 to 360 F for a hot machine.

Once the heat is removed from steam, it condenses to hot water which is called condensate. If condensate is not drained from steam spaces properly, steam consumption is reduced since it cannot enter the water logged spaces and heat output is severely reduced. Proper condensate drainage from a machine is critical to maintain proper heat levels. A typical machine will consume between 6,000 and 9,000 lb/hr of steam depending on speed and grade of product.

The temperature of the condensate formed in machine spaces will be about 375 F. When hot condensate is discharged to atmospheric pressure, 17% of the flow flashes off to steam at atmospheric pressure which is wasted. Without some method to deal with this flash steam, fuel consumption would be 17% higher which amounts to a substantial amount of money in a year. To solve this problem, specialized steam systems have been designed for corrugating machines. Two types of systems have evolved over time, cascade and direct.

Cascade systems can be identified by vertical flash tanks installed along the back side of the machine at each single facer, triple stack heater, and each double backer zone. Salvage steam is used for shower operation. Cascade systems have been offered by Armstrong, United, Langston, and Stickle. Cascade systems operate well but are complex to maintain and trouble shoot.

Direct systems can be identified by a single steam supply, steam traps on each steam space on the machine, and reduced steam pressure fed to the showers. Condensate return can be either low pressure or high pressure design depending on the system. Direct systems have been supplied by S&S, Donahue, and Steamguard.

Either of the two system types can provide acceptable operation. Since most corrugator steam systems have been around for a number of years, we find many systems have been modified from the original design. This modification process combined with the evolution of equipment means that each system generally tends to be somewhat unique from the two general designs.

System Considerations-
A well designed and properly operating system will offer the following:

1. Deliver dry steam at the desired pressure to every vessel.

2. Continuously remove condensate as it forms.

3. Deliver low pressure shower steam to precondition the medium.

4. Provide some means to purge non-condensable gases from the system.

5. Automatically handle large load variations ranging from the machine stopped to producing heavy weight double or triple wall product at high speeds.

6. Start up quickly.

7. Be energy efficient.

If your current system does not meet these criteria, it can be modified to be brought up to current standards at a reasonable cost.

Steam, water and chemical costs are a variable expense and also dependent on monthly production hours. For a typical machine operating 600 hours a month and pulling an average load of 6900 lb/hr (200 HP) of steam, operating details would be as follows:

Fuel costs of $ 51,750 per month at $ 10 per million BTU's
Water costs of $ 99.50 per month at 80% condensate return and water at $ 10.00 per 1000 gallons
Chemical costs of $ 300 per month based on chemical costs of $ 30.00 per 100 gallons

The efficiency of a system can be confirmed by a visual scan. If large amounts of steam vent from the plant and machine, then the current system is inefficient and wasting in the area of $ 7650 per month or ,800 per year. You must also add for the following:

1. Production lost due to a slow machine
2. Scrap and defective product
3. Maintenance down time
4. Excessive machine start up time
5. Customer complaints and losses due to bad product
6. Excessive starch consumption

When all the factors are combined, an improperly operating steam system can cost well in excess of $ 100,000 per year.

Remedies

Either cascade or direct systems can be made to operate properly. For new installations, we favor direct systems as being less costly to install, easier to operate, energy efficient, and better suited to current needs and styles of operation. Any existing system can be modernized at reasonable cost and with excellent payback.

With forty years of hands on experience, Control Specialties can provide a complete range of corrugator system upgrades and improvements at reasonable costs. The improvement process starts with a review of your current installation and production requirements. Once this review is complete, we will provide you with a road map along with costs to improve and upgrade your current system. In many cases systems can be improved in steps to spread costs and further improve payback. Contact us for details.