Principles of industrial production

Commissioning of a new plant

After erection of a new spray drying installation it has to be brought into operation. This phase is called commissioning and proceeds in several stages:

1. Mechanical test of all individual components,
2. Test and calibration of control instruments,
3. Performance test with air,
4. Performance test on water,
5. Performance test on the product(s) for which the spray dryer was designed,
6. Fine tuning of the plant to achieve the design specification (both as to product quality,
7. consumption of energy and capacity),
8. Training of operators, and
9. Final acceptance test and issue of a performance certificate.

Causes for trouble-shooting

If during the intended commissioning period, the specified parameters have not been achieved, efforts are concentrated on how to identify, locate and remove the reasons for the problem. This involves a trouble-shooting exercise conducted as part of the commissioning program. 

However, commissioning is usually finalized successfully to time schedule and the plant quickly in commercial production. In factories faced with their first spray drying installation there has to be a training period during which the factory staff learns how to operate the dryer and the overall behaviour of the plant. However, even in factories having long experience with spray drying and possessing high level of technological knowledge, a training period is still needed, during which both the operators, engineers and maintenance staff acquaint themselves with the new plant since every spray drying installation has its own operational features. The experiences from one spray dryer cannot automatically be applied directly to another one. The development in spray drying has been very fast during the last 20 - 30 years. Therefore an existing spray dryer may not represent the best available technology. 

Experience has shown that problems can occur suddenly even in a well-established, well operated and well maintained plant with experienced staff after many years of successful operation. Such situation is in fact the most typical case calling for trouble-shooting and the problems the trouble-shooter is faced with normally fall into following categories:

1. Lack of capacity 
2. Excessive deposits somewhere in the system 
3. Excessive energy consumption 
4. Product quality defects
5. Excessive powder stack loss 
6. Bacteriological contamination

Production documentation

If a need for trouble-shooting suddenly occurs, the most appropriate approach after briefing about the problem and - if the first routine check of the plant and operation has not brought any explanation - is to find the answers on the above when-what-which questions basis, i.e. to trace when it has appeared and possibly in which consequence. The answers to such questions can be found by interviewing the staff and referring to the records and production documentation. Sometimes it is necessary to go through the documentation of the last few months or even to compare data with the same season of the previous year.

The trouble-shooting is greatly facilitated, if such documentation is readily available and kept intact. 

Production log sheets

It is strongly recommended to keep all production run records containing data written down by the operators with ½ or at least 1 hour intervals. The importance of such practice cannot be emphasized strongly enough, even with modern, computerized plants having full data logging and trend facilities. In the modern electronic data processing it is dangerous to assume that the computer can fully replace the human factor. There are many good reasons to continue with manual operational data recording.

First of all, the tabular type log sheet representing one page for one day operation is easier to survey than a computer print-out. Computer print-outs often involve plenty of paper.

Secondly, it is well known that in modern life direct contact with figures can easily be lost. Therefore an operator, who writes down for 8 hours a day about 20 figures every half hour and does that throughout the whole year, can definitely keep in mind the important parameters better than his colleague just watching a computer screen.

The general rules for keeping production log books are:

1. Separate log-book (or a file of daily log-sheets) for the evaporator and the spray dryer,
2. Separate log-books for each product,
3. Headings describing each production run by type of product, required quality (possibly a number of quality specifications, if any), number of operational parameters specification (if any, see later), the plant configuration (as to optional possibilities which remain unchanged during the operation, i.e. size of nozzle inserts or where fines are introduced etc.), the names of supervisor, operators, laboratory worker responsible for the process control and any other information considered of local importance.
4. A number of vertical columns sufficient to cover the time of reading all the important technological parameters which are shown on the control panel or measured directly by special instruments. It is also very useful to provide columns for the process control of the most important characteristics as final moisture, bulk density, solubility index, and possibly others, as measured by the laboratory or by operators themselves. It is also useful to have some columns expressing the production capacity (as raw milk intake to the evaporator, number of bags or load cell reading of a silo etc.) 
5. Some space has to be reserved as a last column for remarks which serve for comments as to production irregularities, i.e. reasons for production interruptions with stop and restart times, observations as to component malfunctions which did not stop the production (i.e. if a nozzle blocked and had to be replaced), comments as to operator reaction to such irregularities and replies from maintenance staff regarding reported malfunctions (see Fig. 7.2. columns Faults and Repairs: Reported to: Date Repaired:) etc. 
6. A number of rows for interval readings. Intervals should not be longer than 1 hour, preferably ½ hour

General maintenance log book

A log book must be kept to record all service or intervention steps taken with description of the defect and the way the problem was solved. The remarks from the production log book as to malfunction or possible suspicion of malfunction of a component should be followed up by inspection of that component at the next production stop and the results of that inspection should also be recorded. 

It is also very useful to have a check list for control of the various components and to conduct such a control at regular intervals preferably each month. Such control involves, for instance, pressure drops across the air filters, cyclones and perforated plates, checking of thermometer and flow meter readings, safety pressure switches, functioning of the fire extinguishing equipment etc. A visual inspection of state of hygiene not only of the plant but of the whole plant building should belong to the everyday routine checks. 

It is also recommendable to organize a yearly inspection for potential hair cracks and welding failures in the dryer walls. An example of a check list for a small spray dryer with pneumatic transport system is shown on Table.7.1.

Product quality specification

Operational parameter specification

Product quality control

Process quality control

1. Milk acidity at the beginning and end of each tank batch,
2. Concentration from the evaporator,
3. Scorched particles of the powder from the spray dryer (this is mainly for safety reasons
4. indicating a fire risk),
5. Moisture content of the final powder (in the case of a two-stage dryer, also several times
6. during a day the moisture content after each drying step),
7. Solubility index,
8. Bulk density.

Final quality control

1. To follow daily the results of process quality control and its agreement with final quality control,
2. To inform daily the production manager about the quality development,
3. To keep the survey of quality development over longer periods expressing averages and deviations,
4. To control the results of own laboratory by split-sample tests or in cooperation with other, possibly independent laboratories.