+ All Categories
Home > Documents > Experiences with the Balcke-Dürr Falling-Film Plate...

Experiences with the Balcke-Dürr Falling-Film Plate...

Date post: 03-Apr-2019
Category:
Upload: lexuyen
View: 218 times
Download: 0 times
Share this document with a friend
15
Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System EVAP plus List of contents 1. Introduction History of the evaporator development in the sugar industry 2. Construction of the EVAP plus plate pack 3. Function and operation mode Comparison of the falling-film plate evaporator with the falling-film tube bundle evaporator Experiences with the evaporation station of Agrana Hohenau, Austria 4. Cleaning 5. Possible applications of the EVAP plus plate-type evaporator 6. Final remark 7. References
Transcript
Page 1: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Experiences with the

Balcke-Dürr Falling-Film Plate Evaporator System

EVAP plus

List of contents

1. Introduction

• History of the evaporator development in the sugar industry 2. Construction of the EVAPplus plate pack 3. Function and operation mode

• Comparison of the falling-film plate evaporator with the falling-film tube bundle evaporator • Experiences with the evaporation station of Agrana Hohenau, Austria

4. Cleaning 5. Possible applications of the EVAPplus plate-type evaporator 6. Final remark 7. References

Page 2: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

1) Introduction Balcke-Dürr AG is a company with headquarters in Germany which operates worldwide and has a substantial expertise in the fields of power and process engineering. History of the evaporator development in the sugar industry Evaporation stations with four to six effects were normally used in the sugar industry in the past. As the processing capacity of the sugar factories rose, it was necessary to cover the demand for highly efficient evaporators in order to meet the energy requirement.

�����

������

�������������������������������������������������

�������������������������������������������������

�����

������

Tube Plate

Robert

Dec

reas

e of

eff

ectiv

e te

mpe

ratu

re d

iffer

ence

Rising Film Evaporator

Falling Film Evaporator

��������������������

�����������

��������������������

�����������

Development of the evaporators 1840 The Robert evaporator (natural circulation evaporator) was introduced; the Kestner evaporator

(rising film evaporator) followed later. 1967 By using the first falling-film tube bundle evaporator in Germany it was possible to improve

the thermal performance at Südzucker AG. 1987 The first rising film plate evaporators were tested at Britisch Sugar plc in the U.K. and at

Südzucker AG in Germany. 1992 The first falling-film plate evaporator of the EVAPplus type from Balcke-Dürr was put into

successfull operation at Südzucker AG in Germany.

Page 3: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

2. Construction of the EVAPPlus plate pack The technological progress in the fields of welding procedures and deep-drawing of stainless steel; as well as the increasing demand for compact, efficient evaporators led to the development of falling-film plate evaporators. The Balcke-Dürr EVAPplus plate-type evaporator is a combination of a plate heat exchanger with a tube bundle heat exchanger. It is a completely welded plate heat exchanger without seals or gaskets. The shaping of the EVAPplus plate was developed specially for evaporation and condensation applications. The plate pack is composed of shaped, seam-welded stainless steel plates. The special shapings produce two different flow ducts: a tubular and a corrugated profile.

Figure 2 Section of a plate pack

The sugar solution flows down the tubular ducts which are interrupted at regular intervals. This produces a transverse flow on the plate which creates a self-distribution effect. The inflowing steam condenses on the corrugated side. The sugar solution flows on the evaporator surface in cross flow which has a positive effect on the heat transfer rate, the condensate discharge and the removal of noncondensable gases.

The EVAPplus evaporator also differs from conventional evaporators in that its heating chamber is segmented in plate packs placed on top of one another (pack-type construction). This pack-type construction results in the juice flow re-distributing itself on each new plate pack which is approximately one (1) ft (330 mm) deep.

Page 4: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Steam

Condensate

Steam

Figure 3

Segment of the heating chamber

3. Function and operation mode The juice is distributed uniformly from the top through the EVAPplus juice distributor to the plate pack. The juice trickles down from pack to pack as a thin film on the tube side of the heat exchanger plates. The thickened juice and the vapour produced in the evaporation process exit together at the bottom of the plate pack. The steam condenses on the corrugated side. The condensate leaves the steam chamber laterally at the lowest plate pack. The noncondensable gases are removed both at the top and the bottom of the plate pack. Depending on the type of construction, the vapour can be diverted and led upwards to the vapour separator alongside the plate pack. Lamella or centrifugal separation can be used depending on the construction of the vessel shell. In some cases natural separation can also be applied. The thickened sugar solution is collected directly under the pack and fed to the next effect.

Page 5: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Mode of operation of the EVAPplus plate-type evaporator

Vapour outlet

Vapour

Juice

Heatingsteam inlet

Condensateoutlet

Juice outlet

Juice inlet

Vapour outlet

Vapour

Heatingsteam inlet

Condensateoutlet

Juice outlet

Juice inlet

Juice distribution

Juice

Vapour

Vapour

Juice distribution

Heating steam inlet

EVAPplus evaporator

Page 6: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Comparison of the falling-film plate evaporator with the falling-film tube bundle evaporator Colour formation / sugar losses The short residence time of the juice in the evaporator keeps the thermal load on the product to a minimum which means less colour formation and sugar losses. Film thickness / circulation pumps The structure of the EVAPplus plate allows operation with a low juice flow number (juice flow number in l/cm h) – 10% of the value required in the falling-film tube bundle evaporator. This means that either no circulation pumps are necessary (single-pass operation) or considerably lower pump capacity is required. Dimensions / weights Typically stainless steel plates with a wall thickness of 0.6 mm are used in the sugar industry Tube bundle evaporators require a wall thickness of 1.25 - 2 mm. This means a reduction of approx. 50 %, which results in lower weight in addition to better heat transfer. The design of the EVAPplus plate makes it possible to achieve a heating surface density which is up to five times higher. The overall height is also reduced as a result of the compactness. Heat transfer The overall heat transfer coefficient (u-value) is higher not only due to the smaller wall thickness but also because of the plate characteristics and the flow pattern. Depending on the effect, the u-value can be higher than for tube bundle evaporators, with the same temperature difference: from 30 % in the thin juice section up to 250 % in the thick juice section. Figure 7 compares measured u-values of existing evaporators. This means that smaller heating surfaces can be used to produce the same evaporation capacity. For instance, a heating surface of 19.37 ft2 (1.8 m2/t ) can be used for a steam pressure of 43.5 psi (3.0 bar), compared with 30.14 ft2 (2.8 m2/t) of tube bundle evaporators. Figure 5 Comparison of a falling-film plate evaporator and a falling-film tube bundle evaporator with 60,000 ft2 (5950 m2) surface

Page 7: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Heat exchanger type Plate-type evaporator

EVAPplus Tube bundle evaporator

Residence time per effect in evaporator approx.

1.0 - 3.0 minutes 5.0 - 12.0 minutes (Robert up to 20 minutes)

Coverage with liquid

(film thickness) (juice flow number) 0.8 - 1.0 l/cm h 10 - 20 l/cm h

Diameter approx. 45 ft (4.2 m)

39 ft (3.6 m)

Overall height approx. 140 ft (13 m)

270 ft (25 m)

Weight approx. 140,000 lb (70 t)

280,250 lb (125 t)

Wall thickness 0.6 mm 1.25 - 2 mm Heating surface density 73 ft²/ft³

(240 m²/m³) 15 - 27 ft²/ft³

(50 - 90 m²/m³) Overall heat transfer coefficient

u-value 722 - 176 BTU / ft2 h deg

(4100 - 1000 W/m2K) 528 - 71 BTU / ft2 h deg

(3000 - 400 W/m2K) Note : In practice the difference is even greater because the tube bundle evaporators require larger heat exchange surfaces for the same capacity. Experiencies with the new evaporation station of Agrana Hohenau, Austria The technical condition and the high production costs led to the decision to modernize the evaporation station. The 1st to 5th effect are EVAPplus plate-type evaporators with integrated cyclone separator (please refer to Figure 6). An existing falling-film tube bundle evaporator was used as 6th effect. The new EVAPplus evaporation station was installed in the same space as the previous evaporation station. Connection of the evaporation station of Agrana Hohenau The evaporators are all connected in series on the steam side. The evaporation station has two pre-evaporators (4th and 5th effect) on the juice side. The juice system arrangement is: inlet 4th, 5th, 1st, 2nd, 3rd and then 6th effect. The sugar house is supplied with vapour 4 and 5.

Page 8: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Figure 6 EVAPplus plate-type evaporator Agrana Hohenau, Austria

Page 9: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System
Page 10: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Comparison of the evaporation stations before and after modernization

Evaporation station until 1996 Evaporation station

as from 1997

Number of effects 4 6

Evaporator type 6 Robert evaporators

1 Falling-film tube bundle

evaporator

5 EVAPplus plate-type

evaporators

1 Falling-film tube bundle

evaporator

Heating surface 132,180 ft2

(12,280 m2)

242,190 ft2

(22,500 m2)

Space required for

evaporation station

approx.

195,000 ft3

(approx. 5500 m2)

159,000 ft3

(approx. 4500 m2)

Production capacity 10,600 t/h 11,300 t/h

Exhaust steam pressure 56.5 - 59 psi

(3.9 - 4.0 bar)

36.25 psi

(2.5 bar)

Exhaust steam

temperature

289.4 °F

(143°C)

258.8°F

(126°C)

Power consumption 745,057 BTU / t beet

(218.3 kWh / t beet)

615,295 BTU / t beet

(180.28 kWh / t beet)

Page 11: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

Thermal studies The Berlin Sugar Institure was commissioned to measure the operation data. They carried out two series of measurements one in the middle and a second at the end of the 1997 campaign. Figure 6 Operating data of the evaporation station Nov. 1997

Effect 1st 2nd 3rd 4th 5th 6th Steam pressure 37.41 psi

(2.58bar) 32.2 psi

(2.243 bar) 26.21 psi

(1.808 bar) 19.33 psi

(1.333 bar) 16.54 psi

(1.141 bar) 14.83 psi 1.023 bar)

Steam temperature 263.3°F 128.5°C

255.0°F 123.9°C

242.8°F 117.1°C

226.2°F 107.9°C

218.1°F 103.4°C

212.5°F 100.3°C

Vapour pressure 32.52 psi (2.243bar)

26.21 psi (1.808bar)

19.33 psi (1.333bar)

16.54 psi (1.141bar)

14.83 psi (1.023bar)

10.10 psi (0.697bar)

Vapour temperature 255.0°F 123.9°C

242.8°F 117.1°C

226.2°F 107.9°C

218.1°F 103.4°C

212.5°F 100.3°C

193.8°F 89.9°C

Dry substance, inlet 24.10% 32.74% 49.28% 18.14% 21.57% 69.11% Dry substance,

outlet 32.74 % 49.28 % 69.11% 21.57 % 24.10 % 74.95 %

Juice, inlet 258.4°F 125.8°C

256.8°F 124.9°C

246.4°F 119.1°C

212.7°F 100.4°C

219.0°F 103.9°C

235.9°F 113.3°C

Juice, outlet 256.8°F 124.9°C

246.6°F 119.1°C

235.9°F 113.3°C

219.0°F 103.9°C

213.4°F 100.8°C

206.42°F 96.9°C

juice flow number in l/cmx h

2.0 1.3 0.76 3.0 2.6 12.0

Temperature difference

3.6 K 4.8 K 3.8 K 4.0 K 2.6 K 3.4 K

u-value in BTU / ft2 h deg

in (W/m2k)

722.0 (4100)

496.6 (2820)

320.5 (1820)

549.4 (3120)

496.6 (2820)

117.9 (670)

Heating surf. in ft 2 in (m2)

44186 (4105)

44186 (4105)

49094 (4561)

44186 (4105)

39278 (3649)

21528 (2000)

The Agrana laboratory in Tulln, Austria, measured a colour increase of up to 30 %.

Page 12: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

0

1000

2000

3000

4000

5000

u-va

lue

10 20 30 40 50 60 70 80

Brix / wDS, out %

W/(m

²K)

Groningen, Waghäusel, Cantley, Cerekiew *1

(*1 Licha et al. 1994, Morgenroth et al. 1996, 1997, 1998)

u-values Balcke-Dürr Hohenau Factory

Factory Hohenau (2nd trial period)

u-values of Robert and Tube Bundle Falling Film Evaporators

Balcke-Dürr evaporators in

Figure 7 Heat transfer values of the evaporation stations Agrana Hohenau, Suiker Unie Groningen, Südzucker

Waghäusel, British Sugar Cantely, Cerekiew.

4. Cleaning of the EVAPplus plate-type evaporator The EVAPplus plate pack has a self-cleaning effect due to movements of the plate surface (membrane effect). During operation, load changes in the evaporation station cause a large part of the scale to flake off the plate surface. In comparison with other plate-type evaporators, the EVAPplus plate shaping with its tubular ducts and transverse flows has proven advantageous. Broken scale falls down and is entrained with the juice. The heating chamber is cleaned chemically on the juice side, typically by circulation (falling film principle), by recirculating the cleaning liquid. The cleaning liquid depends on the type of scale. In general, alkaline cleaning is carried out after the campaign in order to transform the scale into soluble calcium carbonate. Acid post-treatment with subsequent neutralization make it possible to remove any remaining scale from the heating surface. Sugar charcoal may form when the juice supply is interrupted for a long time and the minimum coverage is not maintained. A cleaning liquid containing special reagents is circulated to remove such incrustations. The heating chamber is flooded and operated in rising-film mode in order to remove any remaining particles. More than 70 % of all EVAPplus plate-type evaporators in operation do not have juice softening equipment. Further details are given in the Balcke-Dürr operating and maintenance instructions. The EVAPplus plate system was originally developed for applications involving pressures of 870 psi (60 bar) and temperatures of 1112°F (600°C), which are substantially higher than those usually found in the sugar industry. In a bursting pressure test carried out in 1995, the plate cracked in the area

Page 13: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

adjacent to the roller seam at approx. 7250 psi (500 bar). In the sugar sector zero leaks have occurred to date. It is possible to plug individual channels (corrugated side) on the steam side similar to tube bundle evaporators. 5. Possible applications of the EVAPplus plate-type evaporator Many sugar factories have capacity bottlenecks because their evaporation stations are too small and not adequate to meet today's processing requirements. This is generally compensated through greater temperature differences and/or higher exhaust steam pressures. This mode of operation means sugar losses (colour) and higher production costs (steam consumption). The replacement of a complete evaporator for higher production capacity (heating surface) is often difficult and expensive. In most cases this means modification of the building, piping, platforms, insulation, structural steelwork and some times foundations. In addition to this, a large crane is necessary. With the "retrofit concept" the EVAPplus plate-type evaporator from Balcke-Dürr offers new opportunities compared to the alternatives which have been used so far to improve existing standard Robert evaporators. Retrofit concept for Robert evaporators A special advantage of the EVAPplus system is the possibility to replace the tube bundle with a plate heating chamber. This can be installed by the sugar factory personnel reducing costs, without large modifications. For instance, a retrofit can be carried out as follows : • Open the semispherical head of the Robert evaporator • Remove the tubes including the tubesheets • Lift the pack tower including the distributor into position. This operation can be carried out in parts

depending on the space and the lifting capacity. • Fix the EVAPplus system by welding the half-moon-shaped and bulkhead plates from the pack

sidewall to the vessel wall. • Existing connections/manholes are reutilized as far as possible; juice inlet, operating vents

(noncondensable gases) and inspection glasses must be correctly welded in position. • Closing of the vessel head and a pressure test complete the retrofit. Depending on the overall height of the Robert evaporator the heat exchange surface can be doubled in most cases. The number of evaporation effects can be increased due to the higher overall heat transfer coefficient (u-value), the larger surface and the resulting smaller temperature difference. This increases the evaporation capacity and can reduce the steam consumption (exhaust steam pressure). Furthermore it is possible to connect other steam consumers to one of the later effects so that the vapour from the first effects can be used to heat the juice in an optimum way. Double-effect evaporator

Page 14: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

EVAPplus plate-type heating chambers arranged on top of one another are ideal for the planning of new factories. The overall height of an EVAPplus double-effect unit is scarcely that of a falling-film tube bundle evaporator with half the heat exchange surface. The design of the double-effect evaporator is analogous with, for example, that of the extraction tower, vertical lime station and crystallization tower.

Figure 8 Double effects

Page 15: Experiences with the Balcke-Dürr Falling-Film Plate ...w.bdheat.com/bd/references/evaporators/experiences.pdf · Experiences with the Balcke-Dürr Falling-Film Plate Evaporator System

6. Final remark For future projects involving modifications or new constructions, the evaporation station Agrana Hohenau has proved that there are new impetus for planners and operators to optimize the production costs in the sugar industry. The EVAPplus evaporation technology makes it possible to increase the capacity of an evaporation station and to reduce the operating costs at a constant total temperature difference. 7. References Austmeyer K.E., 1996: Personal information Doppler, M., Dir. Agrana Werk Hohenau, 1998: Personal information Jonker, W., 1996 Erste Betriebserfahrungen mit dem Balcke-Dürr Platten Fallfilm-Verdampfer in der Zuckerfabrik Suiker Unie Groningen, Rheinisch-Westfälische Zweigverein (VDZ), 29.03.1996 in Cologne Licha, H., Valentin, P., Wersel, M., Witte, G., 1989: Der Plattenverdampfer - ein neuer Weg in der Verdampfertechnik, Zuckerind. 114, 785 - 798 Licha, H., Morgenroth, B., Witte, G., 1994: Operation experience with a falling film plate evaporator, Zuckerind. 119, 257 - 262 Morgenroth, B., Austmeyer, K.E., Mauch, W., 1995 Experience with the Falling Film Plate Evaporator and concepts for energy efficient process schemes in the cane sugar industry, Zuckerind. 120 (ISSCT), 23 - 30 Morgenroth, B., Daschmann, H., Niepoth, K., Abker, G., Schulze, B.-C., 1998: The new falling-film plate evaporator technology in Hohenau sugar factory: Technical development and operational results, Zuckerind. 123, 597-606 Addresses of the authors Klaus Niepoth, Boris Morgenroth, Balcke-Dürr Energietechnik GmbH, D-40882 Ratingen, Hombergerstraße 2, Germany


Recommended