Plant operators should pay particular attention to dryer feed solids when facing challenges with efficiency and capacity in food and dairy spray dryers.
UPDATE: We really appreciate engagement with our audience. On a previous version of this post, a colleague suggested the below outlined viewpoint, and that the opportunity to improve efficiency and capacity may be still greater under certain circumstances. This article is a follow-up post to explain the additional opportunity.
Once again, we value our reader’s feedback, and if you have any topics you’d like to see us write about, please feel free to drop a note and make a suggestion.
Typical food and dairy spray dryers convert concentrated liquids into a free flowing powder, which is accomplished by removing most of the water content via evaporation. This powder can be produced from a variety of concentrates, with both low and high fat and/or protein content.
To operate your process at maximum capacity (powder output), the water removal duty in the spray dryer needs to be minimized. This is always accomplished by operating the dryer at the highest practical feed concentration. Under that condition, the maximum water removal occurs when the dryer feed rate is set according to the following formula:
F = W / (1 – Cf / (100 – Rm) ), where
F = Dryer Feed Rate (lb/hr)
W = Dryer Water Evaporation Rate (lb/hr)
Cf = Dryer Feed Concentration (%TS)
Rm = Powder Residual Moisture (%)
Example: Your dryer was designed to remove 10,000 lb/hr of water (W), Feed concentration is 50%TS (Cf), and the Powder Residual Moisture target is 3.5% (Rm). What concentrate feed rate (F) represents operation at maximum dryer capacity?
F = 10,000 / (1 – 50 / (100 – 3.5) ) = 10,000 / (1- (50 / 96.5) ) = 10,000 / (1 – 0.518) = 20,753 lb/hr
This scenario represents a powder production rate = 20,753 – 10,000 = 10,753 lb/hr
As suggested in earlier comments, this dryer should always be operating at this feed solids level in order to achieve maximum powder output.
Now consider the circumstance that for unknown reasons this same dryer is found to be operating at 45% TS feed concentration. Let’s further assume that this dryer is absolutely limited to 10,000 lb/hr of water removal because the burner system is unable to deliver any additional gas. Under those circumstances, the dryer would be limited to the following duty:
F = 10,000 / (1 – 45 / (100- 3.5) ) = 10,000 / (1 – (45 / 96.5) ) = 10,000 / (1 – 0.466) = 18,738 lb/hr
This scenario represents a powder production rate = 18,738 – 10,000 = 8,738 lb/hr
Unfortunately, this is the best the dryer can do, and this results in 8,738 / 10,753 = 0.81, or 19% less powder output.
If your spray dryer is not currently operating at the maximum practical feed concentration, capacity is being lost. For most facilities, the upstream evaporator is responsible for the low solids condition.
Current evaporator designs have made significant advances with achieving higher concentrations at stable conditions, which can be applied to most existing evaporators. A review of your current conditions can quickly determine the best solution.
Ready to Discuss Dryer Feed Solids for Food and Dairy Spray Dryers?
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