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:
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:
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.
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:
|STATIC PRESSURE mm WG||Temperature|
|Component||Inlet||Outlet||Pressure||Inlet °C||Outlet °C|
|Transport exhaust fan||-230||60||290||42||-|
|Transport exhaust fan||2850||5.5||10||415||-|
|Rotary valve 1||920||0.37||1.3||415||-|
|Rotary valve 2||920||0.37||1.3||415||-|
|Rotary valve 3||920||0.37||1.3||415||-|
|WATER EVAPORATION TEST|
|Test duration (h)||0.5||0.5||TS%||0||43|
|Inlet air °C||167||167||Moisture||-||3.4|
|Outlet air °C||95||95||PGR||12810||12670|
|Amount of feed kg||163||289.9||Evap.-||326||321.7|
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|
|Product:||Instant whole milk powder 28% fat|
|Package:||500g and 2500g tins|
|Property||Value||Method of Analysis|
|Fat content||min.28.2%||NA A9a|
|Titratable acidity||max. 0.15%||NA A19a|
|Insolubility index||max. 0.3 ml||IDF 135-89|
|Bulk density 650x||470-490 kg/m³||NA A2a|
|Fraction > 500µm||max.8.0%||NA A8a|
|Fraction > 125µm||max.20%||NA A8a|
|Free fat content||max.1.9%||NA A10a|
|Sludge 85||max.0.15 g|
|Sludge 20||max.0.15 g|
|Hot water test||max.0.5 ml|
|Coffee test||max.0.5 ml|
|Lecithin content||0.20-0.25%||NA A22a|
|Vitamin A||2500-3000 IU/100g|
|Vitamin D3||500-600 IU/100g|
|Taste||min. 15 points|
|Flavour||min. 15 points|
|Colour||min. 10 points|
|Total plate count||max.5000/g|
|B.coli||neg. in 0.1 g|
|Staphylococcus A.||neg. in 0.1 g|
|Bacillus Cereus||max. 100/g|
|Salmonella||neg. in 500 g|
|Operational Parameter Specification|
|Product:||Instant whole milk powder 28%|
|Heater I temperature||85 °C|
|Holding time||150 s|
|Heater II temperature||by-pass|
|Thermocompressor pressure||5.5 bar|
|Spray dryer||Atomizer wheel||curved vane|
|Atomizer speed||15000 RPM|
|Feed heater temperature||75°C|
|Fines return to:||wheel|
|Homogenizer pressure-total||70 bar|
|Powder moisture ex-chamber||5.5±0.1%|
|Inlet Temperature VF I2)||75-80°C|
|Inlet Temperature VF II2)||60-65°C|
|Inlet Temperature VF III2)||30-35°C|
|Final powder temperature||42-45°C|
|Mixture lecithin/butter oil||1 : 2|
|Wetting agent temperature||65°C|
|Wetting agent dosing - scale||66%|
|In Process Control: 1)||Final powder moisture - IR||2.8±0.1%|
|Bulk density 1250x (volume)||210±5ml|
|1): Conduct every 2 hours if within limits otherwise, every hour|
Handbook of Milk Powder Manufacture
The Handbook of Milk Powder Manufacture is a valuable reference book for dairy processing engineers wanting to take a deeper look at the complex world of milk powder processing.