EP0172965B1

EP0172965B1 - Continuous pan crystallizer

Info

Publication number: EP0172965B1
Application number: EP84305974A
Authority: EP
Inventors: Peter William Rein
Original assignee: TONGAAT-HULETT GROUP Ltd
Current assignee: TONGAAT-HULETT GROUP Ltd
Priority date: 1983-07-22
Filing date: 1984-08-31
Publication date: 1989-03-29
Also published as: EP0172965A1; ZA846920B

Description

This invention relates to continuous pan crystallizers.
Most continuous pans are divided into a number of compartments in an attempt to promote plug flow through the system. For example, GB-A-378 341 discloses a continuous pan crystalliser including a plurality of compartments having calandria and defined by partitions having openings communicating between adjacent compartments. It is important that the flow system approach plug flow as closely as possible, so that crystal residence times in the continuous pan are uniform, leading to equal growth on all crystals and a uniform crystal size in the product massecuite leaving the pan.
One of the objects of the present invention is to provide a system for massecuite to pass from one compartment to another in such a way as to eliminate problems experienced with other types of continuous pans, such as:

(a) short-circuiting or by-passing of massecuite from one compartment to another.
(b) encrustation in the opening between compartments.

In order to overcome the latter problem, steam blowers needed to be installed in some pans at the cross-over ports, to prevent encrustation in the ports. This is expensive and detrimental to thermal economy.
Another object of the invention is to eliminate encrustation of sugar on baffles and other surfaces inside the pan. Such encrustation can lead to the formation of lumps or the dislodging of large pieces of encrustation which can block heating tubes or massecuite outlets.
A subsidiary object is to provide a condenser integral with the pan to reduce the cost of the continuous pan system.
According to the invention there is provided a continuous pan crystalliser of the kind described at the beginning characterised in that the openings are immediately above the calandria and have baffles located on either or both sides thereof.
The massecuite must, therefore, have had at least one pass through the tubes of the calandria before leaving a compartment. Massecuite which passes through a said opening is directed into the downtake area of the next compartment.
The location of the said openings immediately above the calandria has the advantage that the turbulence and vigorous flow obtained in these zones keeps the openings free of encrustation.
A preferred feature of the invention is the provision of very fine water sprays onto all surfaces extending above the normal massecuite operating level. This eliminates any build-up or encrustation on these surfaces, which can otherwise lead to the formation of lumps. Because the quantity of water sprayed through the sprays is very small, it does not affect the control of the supersaturation of the mother liquor in the massecuite and the the crystallisation process is not affected.
As a further preferred feature of the invention, the continuous pan is provided with an integral condenser. This has the advantage of eliminating the costly steelwork and large diameter vapour piping required for conventional separate condensers.
An embodiment of the invention is described below with reference to the accompanying drawings, in which:

Figure 1 is a plan view, partly in section of a continous pan crystalliser according to the invention;
Figure 2 is a side view of the same crystallizer;
Figure 3 is a diagrammatic cross-sectional view of the crystallizer on line A-A of Fig. 2; and
Figure 1A is a detailed plan of heating tubes in one compartment.

In the drawings a continous pan crystallizer includes a plurality of compartments 109 (in this case 12) as shown, having calandria 101. Seed massecuite enters the first compartment and syrup or molasses enters the crystallizer through ports 100. The massecuite passes anti-clockwise from one compartment to the next around the apparatus and leaves it through the outlet 102 (see Figure 3). The openings or cross-over ports 104, 105 between adjacent compartments (1 to 12) each have a pair of baffles 106,108 which are located a short distance from the ports and above the level of the top of the tubes 110 of the calandria. One vertical edge of the baffles abuts the wall of the apparatus and the other is located a short distance inwardly of the vertical edge of the ports. Thus the massecuite leaving a compartment flows up the tubes between the baffle 108 andthe compartment wall, and then through the opening, or port, 104 or 105. It passes through the opening, or port, and then has to negotiate the second baffle 106 on the downstream side of the compartment 109, which directs the massecuite into the downtake.
It will be appreciated that the dimensions and location of the baffles will differ according to the various parameters of the crystallizer and will have to be determined with a view to obtaining optimum plug flow and direction according to pan capacity and evaporation rate.
A preferred feature of the invention involves the installation of fine water sprays, positioned above the normal massecuite level. These sprays are so positioned as to direet a fine spray of water onto some or all of the surfaces of the compartment 109, the deflection baffles 106 and 108, and the internal surfaces of the shell of the vessel.
Another preferred feature of the invention is the provision of an integral condenser generally indicated by reference 112.
The condenser is attached to the top wall of the crystallizer and thereby obviates the expense of the complicated support means which would otherwise be necessary. The condenser has an injection water inlet 114 and a vacuum connection 116 and an injection water outlet 118.
The condenser is conventional, preceded by an entrainment separator 126. The rising vapour is contacted in the consender with a downwardly directed spray of cooling water for collection in a collector 128 for removal through outlet 118.

Claims

1. A continuous pan crystalliser including a plurality of compartments (109) having calandria and defined by partitions having openings (104, 105) communicating between adjacent compartments, characterised in that the openings are immediately above the calandria and have baffles (106,108) located on either or both sides thereof.

2. A continous pan crystalliser according to claim 1, characterised in that a condenser (112) is integral with the pan and in direct communication with the compartments (109).