Dairy Engineering

Module 6. Sterilizing & packing equipment

Lesson 25
CARE AND MAINTENANCE OF STERILIZERS

25.1 Introduction

The sterilizers can be classified as Batch and continuous types, and their maintenance aspects are mentioned below accordingly.

25.1.1 Batch sterilizers

The components that are liable to be damaged over the use and need replacement or recalibration are a) Main door gaskets b) Steam supply valves c) Steam trap d) Water spray nozzles e) Pressure gauges f) Pressure safety valves.

The gaskets are usually of asbestos tape or rope and will get damaged over the period. The correct dimensions of the gasket are important, as well as seating in the groove provided to the closing door. The hinges of the door will need lubrication, to facilitate smooth opening and closing. So are the bolts and levers that ensure tightness of the closure of door. If the sterilizers are of rotating type, then lubrication of the support systems is essential.

Fig. 25.1 Batch sterilizers

Steam supply valves should be leak proof, and if necessary the gland packing has to be replaced. They should be replaced whenever leakage is noticed, to avoid loss of steam and increased cost of operation, and accidents to the operators. The proper operation of steam trap is to be checked from time to time, and there should not be damage due to corrosion or scale formation. Steam pressure gauges must be tested for accuracy, as well as the steam safety valve. Steam safety valves also are susceptible to corrosion and not opening at the required set point. It has to be checked whether any local laws are to be satisfied in their installation or operation. Water spray nozzles should be checked for scale formation and choking.

As the sterilizer operates at high temperature, the insulation and its maintenance are also important. Proper protection and cladding of the insulation whether glass wool or mineral wool is to be taken care of.

Fig. 25.2 Continuous can sterilizer

25.1.2 Continuous sterilizers

In the continuous type of retort systems, the pressure sealing system has to be checked for leakages, and replace the gaskets if necessary. Lubrication of all rotating parts is necessary.

25.2 UHT Plant Operational Care and Maintenance

1. Raw milk quality should be properly tested, and only milk of highest quality must be accepted for UHT processing. The factors of importance are microbiological, flavor related, and adulteration.

2. As much as possible, electrical failure should be avoided, and if in doubt, the plant should be started and operated on standby electrical generator itself.

3. All the precautions for the plant hygiene and personnel hygiene must be observed, in the lines of latest standards of hygiene.

4. Test must be carried out periodically for the plant hygiene, and corrective measures should be immediately initiated.

5. Care must be taken to maintain operative temperatures and pressures inside the heat exchangers, so that there is no formation of vapours and subsequent formation of scale. About 3-4 bar pressure is normal. If 6-8 bars are approached, then stop the plant.

6. Special gaskets will be needed. Nitrile rubber-138°C; Ethylene Propylene Diene Methylene 155 to 160°C is for UHT plants. Right type of fixing material has to be chosen. Also mechanical methods are used for holding the gasket in place.

7. New methods of cleaning and solutions are being used for complete and effective cleaning of deposits especially in heating section. The UHT plant should be provided with CIP line for automatic cleaning operations synchronized with the automation of the UHT plant itself.