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SRI Jigger Tubes System Design, Installation and Commissioning Manual 1.

Introduction This manual details how the SRI Jigger Tubes System can be tailored to suit the needs of a variety of vacuum pans. It provides: Section 2: Section 3: Section 4: Section 5: Section 6: Section 7: Section 8: Section 9: Section 10: Section 11:

2.

Overview of the SRI Jigger Tubes System General design guidelines Fixed calandria batch pans – design examples Floating calandria batch pans – design examples Horizontal continuous pans – design examples Design of inlet piping Construction and installation Control of the noxious gas/vapour flow Onsite technical capability requirements Further technical assistance

Overview of the SRI Jigger Tubes System 2.1 Key distinguishing features The SRI Jigger Tubes System is distinguished from traditional jigger pipe installations in these important ways: •

• •

The jigger tube perforations are small enough to virtually eliminate back-flow of molasses or massecuite, avoiding: o The need for non-return valves. o Blockages of pipework and valving. A wider distribution of very small bubbles results in: o Better circulation improvement. o Minimal risk of tube plate erosion. The SRI system utilises noxious gases withdrawn from the calandria of the pan and places negligible load on the condenser. (Alternatively, process steam or vapour may be used.)

2.2 Physical characteristics The SRI Jigger Tubes System has the following characteristics: • • •

Jigger tubes are 316 stainless steel, 76.2 mm OD, 1.6 mm wall. Perforations are 0.2 mm diameter with about 100,000 holes per lineal metre of tube. Standard tube length 1,500 mm.

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o Shorter lengths quoted and supplied on an individual project basis. o Length recommendations for specific pans allow for cutting and welding, joining to flanges, etc.

2.3 Operational characteristics The SRI Jigger Tubes System is typically fed with noxious gases (incondensible gases) withdrawn from the calandria noxious gas venting system. The jigger tubes are positioned under the calandria, in a pattern designed to distribute a multitude of small gas bubbles into the massecuite over a wide area, at a position that maximises the enhancement of the massecuite circulation. Some vapour accompanies the noxious gases and this passes into the massecuite to boost circulation further. Alternatively, instead of noxious gases, process steam or vapour can be supplied directly to the jigger system. The jigger system would generally operate efficiently on flow rates of gases and vapour at ~15 kg/h/m3 for C massecuite and ~10 kg/h/m3 for high-grade massecuite pans. Commissioning and control are simple. Once the system is commissioned by adjusting the position of a manual valve it does not need to be re-adjusted. No additional control elements are required. 2.4 Replacement for existing jigger systems Some poorly performing or key production pans will already have a jigger system installed. Most such systems inject the jigger feed in localised regions with limited distribution. This sometimes causes erosion of the tube plate and calandria tubes above the jigger feed locations. The SRI Jigger Tubes System can be installed as a replacement system, providing better distribution of the jigger feed and reducing the erosion of the bottom tube plate and calandria tubes.

3.

General installation guidelines In vacuum pans, a strong circulation flow allows the pan to be controlled closer to the optimal supersaturation level and provides benefits in productivity, product sugar quality, and efficiency. Figure 3.1, shows how the injection of noxious gases/vapour in the region underneath the calandria will boost the natural circulation. The SRI Jigger Tubes System is designed to inject the noxious gases/vapour to enhance circulation where it is generally lowest: •

In fixed calandria batch pans, towards the outer periphery of the pan, which also represents the largest calandria tube area per unit radial distance in an annular segment of the pan; and

2

•

In floating calandria batch pans and horizontal continuous pans with the calandria on the longitudinal axis of the pan, towards the centre of the pan, farthest away from the downtake.

Figure 3.1

Illustration of the benefits of the SRI Jigger Tubes System on circulation in a batch pan.

Key design guidelines are: •

For batch pans: o Jigger tubes are constructed from straight tube lengths to form a polygonic ring. o The pitch circle diameter (PCD) of the ring should be about 66% - 75% of the distance across the calandria, from the downtake wall. o The length and number of sides to the ring can be modified to suit. o One noxious gas/vapour inlet is required per 6-8 metres of jigger tube. Where more than one noxious gas/vapour inlet is required, it is recommended that these are equi-spaced around the ring.

•

For horizontal continuous pans: o Jigger tubes are typically installed as tube lengths joined end to end. o One or two rows of jigger tubes are installed underneath the calandria close to the centreline.

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o One noxious gas/vapour inlet is required per row per 6 metres of length. For longer rows, additional inlets should be provided. o The noxious gas/vapour should be sourced from the calandria of the pan module where the jigger row is installed. o Where baffles separating cells/compartments interfere, cut a neat hole in the compartment wall to accommodate the jigger tubes and secure them to prevent vibration. •

4.

General guidelines: o Tube location should take into account: A) Clearance between the pan floor and the bottom tube plate of the calandria. B) Avoidance of feed inlets, cutovers, discharge openings and transducers. o The vertical position of the tubes should allow 50+ mm gap under the tube to the pan floor, to facilitate drainage of massecuite on discharge. o The vertical position should also allow adequate distance for the injected noxious gases to be widely distributed between the top of the jigger tubes and the bottom of the calandria. o The piping inlets to the jigger system will provide support for the tubes. However other supports/saddles will be required, e.g. SS flat plate or stools. These can be bolted or welded in place. o No condensate outlets are required for the jigger tube sections. o Any residual gas or liquid should be sucked into the vessel under vacuum. However, provision should be made to allow the noxious gas feed piping to be drained should the need arise (e.g. for maintenance).

Fixed calandria batch pans - Design examples Figure 4.1 shows an example of the jigger system designed for a typical 120 t fixed calandria pan. The jigger tube ring, each side ~1272 mm, is located on a PCD ~75% of the width of the calandria. The 12-sided ring is easily flanged or welded in sections and offers a near-circular shape. Figure 4.2 shows an alternative arrangement for the flanges. The decision to flange or weld depends on access / clearance / prefabrication issues.

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Flanges between ring sections. Alternatively can be welded insitu.

Downtake wall

Outer wall of pan Two (2) noxious gas/vapour inlets

Calandria

Two (2) noxious gas/vapour inlets

Figure 4.1

Details of the SRI Jigger Tubes System installed in the base of a fixed calandria pan.

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Flanges between ring sections. Alternatively can be welded insitu.

Downtake wall

Outer wall of pan

Two (2) noxious gas/vapour inlets

Figure 4.2

Plan view of the SRI Jigger Tubes System installed in the base of a fixed calandria pan with an alternative arrangement of flanging.

Restrictions such as feed inlets or the presence of openings for cutover pipes may require installation on a smaller or larger PCD (75% of the width of the calandria) to avoid interference. A larger PCD requires more jigger tubes and provides less clearance overhead of the tubes. A smaller PCD requires fewer jigger tubes and provides more clearance overhead of the tubes. However, it will provide less boost to circulation as the noxious gas/vapour will not be injected as close to the outer periphery of the pan. Alternatively, a disjointed ring arrangement can be designed with each section requiring its own inlet as illustrated in Figure 4.3. An external feed ring is required (with isolation valves for each inlet) to provide uniform flow of noxious gas/vapour to the multiple inlets. Disadvantages of this option include additional holes in the pan floor, additional pipe work and valving. This requires more welding on the bottom of the pan, increasing the number of sites at risk of corrosion.

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Syrup /molasses feed risers (6 off 50NB) with 180 mm caps to protect the calandria tube plate sections.

Discharge door Downtake wall

Jigger inlet

Figure 4.3

6 off Jigger tube sections

Plan view of an alternative SRI Jigger Tubes System installed in the base of a fixed calandria pan.

For some pans, the limited room underneath the calandria may result in the jigger ring obstructing/disrupting the massecuite flow patterns within the pan. Two alternatives have been designed for these circumstances: •

Construction of half jigger pipes cut longitudinally and attached on to flat plate and welded to the pan floor. The half pipe protrudes into the gap between the bottom tube plate and the base of the pan to a lesser extent than if a full pipe were used. Benefits include holding back less material on the uphill side of the jigger (if installed as a ring) when the vessel is drained. There is also more space for repairs and maintenance in the outer region of the calandria. Disadvantages include greater system manufacturing costs; and there are many more welds and joins which increase the likelihood of leaks etc. Accordingly, the half pipe installation is recommended only in special circumstances.

•

Arrangement of the jigger tubes in a star pattern. While this provides adequate coverage to the contents within the pan, more noxious gas/vapour feed risers and inlets (plus isolation valves) are needed. This requires more welding on the bottom of the pan, increasing the number of sites at risk of corrosion. An external feed ring is also required to provide uniform flow of noxious gas/vapour to the multiple inlets. The star type jigger system is shown in Figure 4.4.

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Downtake

Jigger tubes

External noxious gas/vapour feed ring

Calandria

Manual isolation valve Figure 4.4

5.

Noxious gas/vapour riser and inlet

Details of the star pattern SRI Jigger Tubes System design for a fixed calandria pan.

Floating calandria batch pans - Design examples Figure 5.1 shows the jigger system designed for a typical 80 t floating calandria pan with a centre steam entry. For floating calandria batch pans, the PCD of the jigger ring should be positioned at about 25% to 33% of the width of the calandria. As most floating calandria batch pans have a centre steam entry (which doubles as a support structure for the calandria), the width of the calandria is specified as the distance from the outer edge of the steam entry (or the surround pipe) to the downtake wall. For floating calandria pans with a non-centre steam entry, the width of the calandria is measured from the outside of the blank tube plate on the centreline of the pan to the downtake wall.

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The system in Figure 5.1 comprises a ring located on a centreline ~27% of the width of the calandria and requires four lengths of jigger tube of 1500 mm each to be cut into ~750 mm lengths to allow a more circular eight sided ring to be manufactured. The jigger ring can be flanged or welded in sections (Figure 5.1 shows the jigger tubes welded together). The decision to flange or weld the jigger ring will depend on whether the jigger ring will be installed in situ. This is dependent on the clearance of the downtake and access through the manholes/discharge openings.

Jigger ring

ia dr n la Ca

Downtake wall

th id w

Steam entry Jigger inlets (2 off) Pan feed inlets

Outer wall of pan

CALANDRIA

Jigger inlets (2 off)

Figure 5.1

Steam entry

Pan feed inlets

Details of the SRI Jigger Tubes System installed in a floating calandria batch pan.

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Restrictions such as feed inlets or cutover pipes at the location of the jigger ring may require its installation on a larger PCD to avoid interference. Ideally the PCD would be less than 33% of the width of the calandria. Installing the ring on a smaller PCD may not be suitable as the jigger system will be very close to the centre steam entry. Installing the ring on a larger PCD would require more jigger tubes and likely be less effective in boosting circulation. For floating calandria pans where interference with discharge openings and/or cutovers exists, a disjointed ring arrangement could be designed with each section requiring its own inlet as illustrated in Figure 5.2. The external noxious gas/vapour feed pipe work would need to be designed to provide uniform flow to the multiple inlets.

Ca

la

nd ria

wi

dt

h

Jigger inlets (2 off)

Cutover pipe

Discharge door

Jigger sections (2 off) Pan feed inlets

Outer wall of pan

Figure 5.2

Downtake wall

Plan view of an alternative SRI Jigger Tubes System design for a floating calandria pan.

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6.

Horizontal continuous pans - Design examples For horizontal continuous pans without a longitudinal partition to divide the compartments, a single row of jigger tubes, preferably located underneath the calandria and axially along the centreline, is recommended. This arrangement is shown in Figure 6.1. For continuous pans with a longitudinal partition, or inadequate clearance underneath the calandria at the centre location, or when feed risers interfere along the centreline, a row of jigger tubes should be installed longitudinally on each side of the centreline and offset from the centreline by ~12% to 15% of the width of the calandria. This arrangement is shown in Figure 6.2. The jigger rows can extend for the length of a module in the pan (length reduced by a small distance at each end of the module). Depending on the design of the pan, this may involve providing cutouts for the jigger tubes to pass through compartment walls. Note:- A module is defined as a section of the pan that contains a separate calandria. Some pans, e.g., FCB pans with heating tubes that extend the full length of the pan comprise one module. SRI continuous pans typically comprise two or three modules. The jigger rows can be flanged or welded within the module. Feed inlet or cutover pipe restrictions can be overcome by positioning the rows of jigger tubes around them.

Steam entry

Calandria width

Calandria

Inlet for jigger

Figure 6.1

Outer wall of pan

End view of the SRI Jigger Tubes System installed as a single row on the longitudinal axis in a horizontal continuous pan.

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Steam entry

Calandria width

Calandria

Jigger tubes run axially

Figure 6.2

12-15% of calandria width

Inlet for jigger

Outer wall of pan

End view of the SRI Jigger Tubes System installed as a double row in a horizontal continuous pan.

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7.

Design of inlet piping The more common options for installing the inlets to the SRI Jigger Tubes System are illustrated in Figure 7.1 and include: (a) Welding a mild steel pipe (80NB) and tee piece (80NB) at the inlet location with mild steel flanges on the ends of the tee piece. A mild steel flange is also attached to the mild steel pipe external to the pan to connect to the noxious gas/vapour feed pipe. This may not be necessary if the noxious gas/vapour feed pipe is hard plumbed. The jigger tubes with their own stainless steel flanges can be attached to the flanges on the ends of the tee piece as illustrated in Figure 7.1. This option eliminates the need to weld stainless steel to the mild steel pan floor. Suitable flanges would be Table D or Table E. (b) Welding a mild steel pipe (80NB) and flange just inside the pan at the inlet location. A mild steel flange is also attached to the pipe external to the pan to connect to the noxious gas/vapour feed pipe. A stainless steel flange and tube tee piece (76.2 mm) can be attached to the mild steel flange inside the pan as illustrated in Figure 7.1. The jigger tubes are welded to each side of the stainless steel tube tee piece. This option does not require welding stainless steel to the mild steel pan floor. Its suitability will depend on the available clearance between the pan floor and the calandria at the inlet location. Suitable flanges would be Table D or Table E. (c) A circular or square section is removed from the pan floor at the jigger inlet location. A thicker (36 mm) mild steel plate is then welded to replace the removed section. The thicker plate has tappings drilled to allow a stainless steel flange connected to the jigger tube system to be bolted to the pan floor. The thicker plate will make it easier for welding inside the pan and also has a flat base rather than the slightly curved surface of the pan floor. Suitable flanges would be Table D or Table E. The noxious gas/vapour feed risers in the pan for the jigger system can be of a slightly smaller diameter than the 80NB specified in Figure 7.1. Standard 80NB tee pieces also do not need to be used for the jigger inlets. A non-standard 80NB tee piece utilising smaller inlet sizes such as a 65NB or 50NB connection for the noxious gas/vapour inlet piping should be sufficient for some installations. Alternatively the noxious gas/vapour feed pipe can be welded into the bottom of the jigger tube thus forming a tee piece.

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Calandria

Calandria

Pan floor

Pan floor

Rotated and enlarged Stainless steel flange

Rotated and enlarged

Mild steel flange

Jigger tube

Jigger tube welded Stainless steel tee piece 76.2mm to tee piece

Mild steel tee piece 80NB

Stainless steel flange

Mild steel flange Mild steel pipe 80NB

Pan floor

Pan floor

Mild steel flange (external to pan)

Mild steel flange (external to pan)

(a)

(b) Calandria

Pan floor Rotated and enlarged

Stainless steel tee piece 76.2mm

Jigger tube welded to tee piece

Stainless steel flange Mild steel plate with taps

Pan floor

Mild steel pipe 80NB Mild steel flange (external to pan)

(c) Figure 7.1

Details of installation options for the inlets of the SRI Jigger Tubes System.

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8.

Construction and installation Figure 8.1 shows a typical layout for transferring the noxious gas/vapour from the calandria to the jigger system in the base of a fixed calandria batch pan. The arrangement of the pipe work connections for floating calandria batch pans and horizontal continuous pans is similar. TO CONDENSER or ATMOSPHERE

NOXIOUS GAS / STEAM LINE

MAX. BOILING LEVEL

VALVE FOR REGULATION OF THE NOXIOUS GAS/VAPOUR FLOW

CALANDRIA

JIGGER RING INLET/S VALVE FOR EACH INLET

TO OTHER INLETS OF JIGGER SYSTEM SOCKET FOR PRESSURE MEASUREMENT

Figure 8.1

Proposed valving and instrumentation for the SRI Jigger Tubes System.

A noxious gas/vapour pipe will need to be installed from the takeoff point (source) outside the pan and above the calandria to beneath the pan and split to the inlet/s of the jigger system. The pipe may need to be insulated for safety reasons. The suggested installation procedure involves using a manual valve (i.e. globe/gate valves) close to the noxious gas source (positioned conveniently for the operator) and other valve/s (i.e. ball valves) close to the noxious gas/vapour inlet/s on the base of the pan as shown in Figure 8.1. The two sets of valves can be used to isolate the jigger system from the noxious gas/vapour source and the pan, if required. The valve close to the noxious gas source will enable adjustment of the quantity of noxious gas/vapour fed to the pan. The other valve/s should be located as close as possible to the noxious gas/vapour inlets on the bottom of the pan for isolation reasons. During normal operation these bottom valve/s will remain fully open. The bottom valve/s close to the noxious gas/vapour inlets do not need to be closed between pan cycles. If the jigger system is isolated, necessary pipe work should

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allow the noxious gas/vapour line to be vented to its previous destination (i.e. to the condenser or headspace) or to atmosphere. A socket (25NB) should be installed as close as possible to the noxious gas/vapour inlet to the bottom of the pan to enable a pressure measurement at this point. A manual valve (ball valve) should be installed on this socket. This socket could also be utilised for cleaning/draining purposes and should be located at the lowest part of the noxious gas/vapour inlet line. (Note: The pressure at the socket will be less than atmospheric pressure when the pan is operating under vacuum.) In constructing and installing the jigger system into a vacuum pan the following procedure is recommended: 1. Determine the exact design and location of the jigger system within the pan, including the type of inlet design. 2. Draw/sketch the jigger system to be installed within the pan to check clearances within the pan underneath the calandria and interference with feed inlets, discharge openings, cutover pipe work, instrumentation etc. 3. Construct the jigger ring and lay the ring out external to the pan. The sections of the jigger tube system should be connected as if they were installed inside the pan. (i.e flanges connected or if the ring is to be welded in situ, then spot welds should hold the jigger tube sections together. (Note: The jigger tubes can be cut and welded through the perforated section. The splatter from welding will close off some perforations but the effect on the operation of the jigger system is negligible because of the large number of holes in the adjacent section.) 4. Based on the layout of the jigger ring, accurately measure and locate the centres for the inlets in the pan base. 5. The inlet holes to the base of the pan can be cut (drilled) and the inlets attached to the pan base. 6. The layout for the noxious gas/vapour feed pipe work should be determined to ensure limited congestion around and underneath the pan and a similar flow rate of noxious gas/vapour feed is provided to each of the jigger inlets. This will be achieved by installing a symmetrical pipe arrangement to the noxious gas inlets under the pan. This will include providing an easily accessible manual valve close to the noxious gas/vapour source, isolation valves beneath the pan close to each jigger inlet and a socket close to a jigger inlet for calibration measurements. 7. The noxious gas/vapour feed pipe work can then be connected to the jigger inlet at the base of the pan. This will include installation of the manual valves and measurement socket near the inlet. 8. Safety concerns may require the noxious gas/vapour pipe work to be insulated. The noxious gas/vapour source should be isolated during completion of this pipe work. 9. The jigger tube system can be installed and connected in the pan. This will include providing appropriate supports/saddles for the tubes. All welded surfaces should be cleaned and ground smooth on completion. 10. The settings of the manual valve to regulate the noxious gas/vapour feed will need to be determined when the jigger system is commissioned.

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Note: Steps 3 and 4 will not be necessary for the installation of jigger systems in horizontal continuous pans. If flanges are used in the design of the jigger feed inlets then blank flanges can be connected on the flanges inside the pan. The construction and installation of the jigger tube system in the pan can proceed independently of the construction and connection of the noxious gas/vapour feed pipe work. Welding advice Generally mild steel and stainless steel materials can be welded with confidence to provide structural support. The acidic nature of sugar solutions can cause a slight galvanic reaction (corrosion) if mild steel and stainless steel surfaces are welded together, thus reducing the life of welds. For this reason, the number of welds between mild steel and stainless steel surfaces should be minimised. Preparation of the welding site and materials is one of the most important factors to ensure weld integrity. Preparation includes preheating the tubes before welding and cleaning both the weld joint area and the filler metal. On completion of the welding (stainless steel or mild steel) the slag and weld area should be ground smooth to remove possible sites for initiation of corrosion. Insulation kits for flanges and saddles can be utilised in the construction of the jigger systems to ensure that mild steel and stainless steel surfaces do not need to be welded together or contact each other. Other recommendations for construction of the jigger systems include: •

•

•

9.

Drill the holes for the jigger inlets in the base of the pan rather than oxy-cutting for a: o Neater fit for the inlet pipe; and o More structurally stable weld. If connecting stainless steel pipe to the bottom of the perforated jigger pipe (rather than a separate tee piece), use a hole saw rather than a plasma cutter to cut the entry hole on the underside of the jigger tube to prevent splatter blinding off some of the laser-cut perforations. If welding stainless steel to mild steel surfaces, stronger welds are achieved with thicker surfaces (e.g. for small sections of stainless steel flat plate to support the jigger system above the pan floor). Full pen butt welds are preferred.

Control of the noxious gas/vapour flow The description below refers to setting the noxious gas/vapour flow of the jigger installation for the fixed calandria batch pan shown in Figure 8.1. The control procedures are similar for other installations (e.g. into floating calandria batch pans and horizontal continuous pans). The flow rate of noxious gas/vapour to the jigger system is regulated by the manual globe/gate valve set to an appropriate number of turns. A pressure differential of 10 to 20 kPa (between the noxious gas/vapour inlet and the pressure within the massecuite at the base of the pan) during operation should give an adequate flow. The isolation

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valves (for the inlets to the jigger system) at the base of the pan should be fully open when the appropriate setting is determined for the regulating valve. The two isolation valves are left open during normal operation. During commissioning, the regulating valve should be adjusted to the setting that ensures: • •

All incondensible gases are withdrawn from the calandria steam chest; and The quantity of steam withdrawn with the noxious gases is not excessive.

It may be necessary to increase the steam flow rate to the calandria when operating the jigger system if additional steam is withdrawn with the noxious gases to boost the pan’s performance. This may be necessary in poorly performing (poorly designed) pans. The procedure for setting the noxious gas/vapour flow to the jigger system is as follows: 1. The pan should be boiling massecuite at the normal operating vacuum. For batch pans, the boiling level may be reasonably low when the initial set up is undertaken (low level is not essential). 2. Open the jigger system isolation valves below the pan (fully open). 3. Open the valve on the socket near the feed inlet and check a vacuum exists at this point. 4. Close the valve and install/connect a pressure transducer/gauge. The transducer should be suitable for measuring sub-atmospheric pressures. 5. Through sight glasses on the pan, observe the boiling action and movement of massecuite at the boiling surface from above the calandria to the downtake. 6. Close the valve directing the noxious gases from the calandria to the headspace (condenser) or atmosphere and open the regulating manual valve a few turns. 7. Observe the pressure on the transducer. For a pressure difference across the perforations of 15 kPa the pressure at the transducer will be typically 55 kPa abs to 75 kPa abs (or a value ~15 kPa higher than the transducer reading when the regulating manual valve is closed). It is necessary to calculate the desired pressure for the particular installation. Appendix A provides the details of the calculation procedure. 8. Observe the boiling action of the massecuite through the sight glasses. The injection of the noxious gas/vapour through the jigger system will not cause a massive eruption of massecuite. The changes will appear relatively gentle with an improved circulation flow in the massecuite being evident. Note: At higher operating levels in batch pans the main circulation path is below the massecuite surface and changes to the jigger gas injection are likely to be less visible through the sight glasses. 9. When the batch pan is at the full condition and is nearing heavy up, the required pressure value (for 15 kPa difference across the jigger perforations) should be calculated and the regulating manual valve adjusted to achieve this pressure. The setting of the valve (number of turns of opening) should be determined and noted. If possible, examine the boiling action in the pan (generally difficult when batch pans are full).

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Note: For batch pans, it is generally preferable to set the noxious gas/vapour flow (by setting the opening of the regulating manual valve to provide a 15 kPa pressure difference) when the pan is at the pan full, near heavy up condition as this is the condition for which the boost to circulation is most important and beneficial. 10. Leave the regulating manual valve in its current position and the valves below the pan should be fully open. 11. For the next pan strike observe the boiling in the pan with the regulating manual valve at this opening. If the boiling action looks satisfactory then the commissioning of the jigger system is completed. 12. Remove the pressure transducer (optional). 13. If further adjustments are thought necessary, repeat the set up procedure. For example, operation with a 20 kPa difference in pressure could be trialled to select the preferred operating set up. Note: For horizontal continuous pans, with constant and lower static level of massecuite above the jigger tubes, the jigger system will operate effectively at a lower pressure difference across the perforations (e.g. 10 kPa difference in pressure may be appropriate). Automatic control of the pressure differential is not required and once the setting of the manual regulating valve is determined to provide a pressure differential of 10 to 20 kPa the valve can be left in this position. There is no need to change the setting of the valve. The individual valves on the noxious gas/vapour feed inlets can be used for isolation when the jigger system is turned off. Experience with the system in vacuum pans shows that there is negligible flow of ‘syrup’ back into the jigger pipes and so these valves would be left open apart for exceptional circumstances, e.g., pan shut down during a maintenance stop.

10. Onsite technical capability requirements To construct and install the SRI Jigger Tubes System in vacuum pans, factory staff will require knowledge of, and competent training on, the following: • • • •

Welding in confined spaces Pressure vessel welding practices Stainless steel and mild steel welding procedures Basic control instrumentation practices

11. Further assistance Contact:

ActionLaser Pty Ltd Attn: Steve Morris or Paul Segner

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Address:

PO Box 1926 Hornsby-Westfield 1635 Australia

Telephone:

Int + 61 2 9476 3790

Facsimile:

Int + 61 2 9476 6993

e-mail:

[email protected]

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Appendix A Setting the appropriate flow rate of noxious gases/vapour (For Clients)

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Example of pressure differential calculation for a fixed calandria batch pan. (a) Determine the pressure on the top of the jigger tube at the bottom of pan (labeled Pmass in Figure A.1). The calculation requires the vacuum pressure (Pvacuum), level of massecuite in the pan above the top of the calandria, and distance of the top of the jigger tube below the top of the calandria to be measured or determined. (b) Determine the target pressure (assuming a 15 kPa pressure differential from inside to outside the jigger tube) in the noxious gas/vapour feed inlet to the jigger system (as measured at the socket close to the inlet and labeled Pjigger in Figure A.1). Figure A.1 shows the typical arrangement of the jigger system in a batch fixed calandria pan. TO CONDENSER or ATMOSPHERE

Pvacuum 15 kPa abs NOXIOUS GAS VALVE FOR REGULATION OF THE NOXIOUS GAS/VAPOUR FLOW

BOILING LEVEL 1000 mm

CALANDRIA

1000 mm

300 mm

Pmass VALVE FOR EACH INLET TO OTHER INLETS OF JIGGER SYSTEM

Figure A.1

Pjigger

Schematic of pan illustrating information for pressure calculations.

Variables: • • •

Headspace pressure of 15 kPa abs [vacuum -86 kPa g]. Operating level of 1 m above the top of the calandria. Jigger tube is 1.3 m below top of calandria (i.e. calandria tubes 1 m long and 0.3 m clearance under calandria to the jigger inlet).

1

Calculations: Ignoring the effect of vapour bubbles in the massecuite, the density of massecuite is assumed to be 1.45 t/m3. Static Pressure due to head of massecuite on top of the jigger tube = density of massecuite * gravity * height Static Pressure = 1.45 t/m3 * 9.8 m/s2 * (1+1.3) m = 33 kPa Absolute pressure at the top of the jigger tube (Pmass) = Headspace pressure (Pvacuum) plus pressure due to head of massecuite on top of the jigger tube = 15 + 33 = 48 kPa abs Target absolute pressure at the inlet to the jigger pipe (Pjigger) = Pressure at the top of the jigger tube (Pmass) + pressure differential = 48 + 15 = 63 kPa abs

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