**3.3 Results and discussion**

546 Heat Exchangers – Basics Design Applications

Fig. 10. Pilot plant used for practical tests (Institute of Food Quality LUFA-Oldenburg-

The plate heat exchanger, in which coated and uncoated plates can be installed, consists of two cooling sections (deep cooler with 8 plates and pre-cooler with 10 plates), heat recovery section (with 12 plates), heating section (with 7 plates) and hot water section (with 6 plates). Before assembling the heat exchanger, selected plates in the heating and heat recovery sections were coated using the method described in section 3.2.1. As a reference, stainless steel, electro-polished and PTFE coated plates were also installed in the heat exchanger

Germany) with GEA Ecoflex VT04 plate heat exchanger.

(Figure 11). Table 6 details the samples used and their specifications.

Fig. 11. Plates layout inside GEA Ecoflex VT04 plate heat exchanger.

Technical investigations were carried out by IUV and LUFA on the deposits formed from whey protein solution in both the laboratory facility and the pilot plant.

#### **3.3.1 Laboratory tests by IUV**

Laboratory investigations were carried out by IUV on the deposit of whey protein on the tube surface. Different stainless steel tubes were tested by IUV using the laboratory heat exchanger apparatus described in section 3.2. Figure 12 shows the deposit accumulation rates of whey protein solution for the different tube surfaces.

Fig. 12. Deposit accumulation rates for laboratory tests with whey protein on small coated cylindrical ducts. Plate characteristics are given in Table 6.

Fouling in Plate Heat Exchangers: Some Practical Experience 549

Figure 14 shows photographs for two different coated plates from the heating section in the

It is evident that the coatings have been locally destroyed at the contact points, as pointed by the red circles in the figure. The flow in the plate gap causes relatively high vibrations with particularly strong stresses to the contact points, which is added to the high thermal stresses. The coatings at the present stage of development could not withstand these stresses

Fig. 14. Coated heat exchanger plates from heating section: (a) A2 coating, (b) A10 coating.

Nano-composites could be used as anti-fouling coatings to decrease fouling inside gasketed plate heat exchangers for the dairy industry. Industrial tests showed that the coatings A2 and A10 reduced fouling, though the PTFE coating showed higher fouling than the standard stainless steel plate. The deposit buildup on the electro-polished plates was lower than the standard stainless steel plates and almost comparable to the coated plates. A CIP time reduction was observed for all coatings: PTFE coated plates down by 90%; nano-composites coated plates down by 70%; electro polished plates down by 36%. Pilot plant testing indicated the coatings must be further developed so that they can withstand the thermal and

mechanical stresses which arise in industrial operation.

IUV Institute of Environmental Process Engineering

EP Electrically-polished stainless steel

INM Institute of New Materials

LUFA Institute of Food Quality

PCTFE Polychlorotrifluorethylene PHE Plate heat exchanger

PTFE Polytetrafluorethene (Teflon)

heat exchanger after different experimental runs (A2 on left and A10 on right).

and need further development.

**3.4 Conclusions** 

**4. Nomenclature** 

CIP Cleaning in place

NT New technology

SS Stainless steel VT Varitherm

XRF X-ray Fluorescence

The Polyurethane-coated tubes gave the thinnest deposit layer, closely followed by the electropolished tubes. The laboratory cleaning tests showed that under the same hydrodynamic conditions, the cleaning time for test tube A9 is only 20% of that needed for the standard stainless steel tube.

#### **3.3.2 Pilot plant tests by LUFA**

In a test series LUFA Nord-West in Oldenburg-Germany examined the formation of deposit on test PHE plates which had undergone different treatments. Different coated plates were installed in the heating section of a pasteurizer, with PTFE coated plates next to electropolished and standard stainless steel plates. The anti-fouling coatings were high-molecular polymers with implanted nano-particles which resulted in high hardness and scratch resistance. The pasteurizer was operated with a 10% (by weight) whey protein solution which was heated up to 85°C. Figure 13 shows the amount of residue, in g, for different surfaces in three tests. It is noteworthy that in these test conditions there is significant whey protein deposition on uncoated, electro-polished and A2-coated stainless steel.

The coatings A2 and A10 showed reduced deposit buildup (the PTFE coating gave more deposit buildup than the standard stainless steel plate). The plates coated with A10 coating had the lowest adhesion, which was similar to the laboratory test results. The deposit buildup on the electro-polished plates was lower than the standard stainless steel plate and almost comparable to the coated plates. Cleaning studies indicated that the cleaning in place (CIP) time, for all coatings was shorter than that for the standard stainless steel plate: PTFE coated plates down by 90%; coated plates down by 70%; electro polished plates down by 36%.

Fig. 13. Amount of deposits formed using whey protein solution, in three tests (m2, m3 and m4).

Figure 14 shows photographs for two different coated plates from the heating section in the heat exchanger after different experimental runs (A2 on left and A10 on right).

It is evident that the coatings have been locally destroyed at the contact points, as pointed by the red circles in the figure. The flow in the plate gap causes relatively high vibrations with particularly strong stresses to the contact points, which is added to the high thermal stresses. The coatings at the present stage of development could not withstand these stresses and need further development.

Fig. 14. Coated heat exchanger plates from heating section: (a) A2 coating, (b) A10 coating.
