Abstract:
A system and a method are provided for melting solid sulfur and maintaining the resulting molten sulfur in liquid state. The system and the method may be fabricated, installed and operated at low capital costs, with high throughput rates at high operating efficiencies and low maintenance costs. Specific embodiments of the invention include modular and non-modular designs, which may be installed and operated with low to high degrees of automation, allowing the user to tailor the final configuration to meet specific requirements. The system of the invention comprises a specific configuration of a prescribed solid sulfur feed unit, a prescribed high-capacity melting unit, a compartmentalized pump tank assembly, and a heat exchanger located outside the high-capacity melting unit. The method provided follows the configuration of the system.

Description:
[0001]    This application is a non-provisional application for patent entitled to a filing date and claiming the benefit of earlier-filed Provisional Application for Patent No. 61/742,511, filed on Aug. 13, 2012 under 37 CFR 1.53 (c). 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a system and a method for melting sulfur and, specifically, to an improved system and an improved method for melting solid sulfur and maintaining the resulting molten sulfur in liquid state. More specifically, the invention relates to safe sulfur melting methods and systems that may be fabricated, installed and operated at low capital costs, with high throughput rates at high operating efficiencies and low maintenance costs. Specific embodiments of the invention include modular and non-modular designs; and the invention may be installed and operated with low to high degrees of automation, allowing the user to tailor the final configuration to meet specific requirements. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional techniques for melting sulfur often involve mixing crushed, formed or otherwise solid sulfur with liquid sulfur in a tank that has been kept at temperatures above the melting point of sulfur and maintaining the contents of the tank at such temperatures by heating means. Crushed solid sulfur normally originates from solid sulfur lumps and from solid sulfur storage blocks, commonly known as “sulfur vats”; formed solid sulfur usually comes from special industrial operations designed to make specific forms of solid sulfur, such as slate sulfur and sulfur prills, sulfur pellets sulfur pastilles and other such types of granulated sulfur, which are intended for later melting and use as sulfur feed material in various industrial processes. At atmospheric temperatures sulfur is solid; and it remains solid as long as its temperature remains below approximately 240° F.; above this temperature sulfur becomes a fairly fluid liquid; and it remains a relatively low-viscosity fluid until its temperature reaches about 318° F. Above 318° F. sulfur turns very viscous and becomes difficult to pump. 
         [0004]    A process for melting sulfur is described in U.S. Pat. No. 3,355,259, of Lipps et al, in which solid sulfur is fed into a tank and mixed with molten sulfur that has been maintained in liquid state at temperatures between 238° F. and 320° F. by the introduction of hot combustion product gases at certain points below the surface of the molten sulfur. This technique has had some commercial applications in the past, but its use is not cost efficient nowadays for various reasons, among them the additional costs required to monitor, process and control the hot combustion product gases in order to maintain the emissions within current environmental discharge requirements. In addition, the combustion product gases introduce contaminants into the liquid sulfur which translate into additional purification costs downstream and/or in the subsequent processing of the molten sulfur product. Certain other known processes for melting sulfur accomplish the melting by providing a melting vessel and introducing steam coils inside the vessel. These processes are able to produce molten sulfur but their overall efficiencies are limited by the limited heat transfer surface area and the size of the vessels that such arrangements entail. 
         [0005]    It is an object of the present invention to provide a system and a method for melting sulfur that do not introduce into the molten sulfur any hot combustion gases or any other external sources of heating media, thus avoiding the cost efficiency disadvantages and the contamination problems associated with processes such as the Lipps et al process. It is also an object of this invention to provide a system and a method for the effective melting of crushed or formed solid sulfur that expedite and improve the removal of underflow solids from the tanks where most of the melting takes place and that do not require the introduction of steam coils inside the melting vessels. Another object of the invention is to provide safe sulfur melting methods and systems that may be fabricated, installed and operated at low capital costs, with high throughput rates at high operating efficiencies and low maintenance costs. A further object of the invention is to provide a practical and efficient system and a practical and efficient method for melting solid sulfur that lend themselves to modular fabrication and factory-assembly for easy and cost-effective shipping and on-site assembly. Yet another object of the invention is to provide a system and a method for the effective melting of solid sulfur that allow all of the molten sulfur to be safely contained during unplanned shutdown periods and where all of the vessels and equipment are located above ground, thereby eliminating or minimizing water intrusion, heat losses and other maintenance problems associated with systems and methods that locate vessels or equipment below ground. Still another object of the invention is to provide a system and a method for melting sulfur that allow the flexibility of processing both low and high volumes of solid sulfur feeds without sacrificing either safety or cost effectiveness. An additional object of the invention is to provide a system and a method for the effective melting of solid sulfur that can be industrially fabricated, installed and operated with minimal or no environmental consequences. These and other objects of the invention will become apparent from the descriptions that follow. 
       SUMMARY OF THE INVENTION 
       [0006]    The system and the method for melting sulfur of this invention are described below with reference to their various system components and method steps. In its broadest embodiment the system of the invention comprises a combination of the following specific components: (a) a high-capacity melting unit; (b) means for pumping molten sulfur; and (c) a heat exchanger located outside the high-capacity melting unit and provided with means for heating pumped molten sulfur to a temperature of between about 275° F. and about 350° F. and returning it to the high-capacity melting unit. In one preferred embodiment the system of the invention comprises a specific arrangement of the following components: (a) a solid sulfur feed unit; (b) a high-capacity melting unit; (c) a compartmentalized pump tank assembly; and (d) a shell-and-tube heat exchanger located outside the high-capacity melting unit. In its broadest embodiment the method of the invention comprises a combination of the following specific steps: (a) receiving and melting solid sulfur in a high-capacity melting unit; (b) pumping the molten sulfur to a heat exchanger located outside the high-capacity melting unit; and (c) heating the pumped molten sulfur in said heat exchanger to a temperature of between about 275° F. and about 350° F. and returning it to the high-capacity melting unit. In one preferred embodiment the method of the invention comprises a specific arrangement of the following steps: (a) feeding solid sulfur to a high-capacity melting unit; (b) melting the fed solid sulfur in the high-capacity melting unit; (c) processing the molten sulfur through a compartmentalized pump tank assembly and pumping it to a shell-and-tube heat exchanger located outside the high-capacity melting unit; and (d) heating the processed and pumped molten sulfur in said shell-and-tube heat exchanger to a temperature of between about 275° F. and about 350° F. and returning it to the high-capacity melting unit. 
         [0007]    The solid sulfur feed unit of the invention comprises a bulk solid sulfur feed hopper and a solid sulfur feed conveyor (sometimes referred to herein as the “melter feed conveyor”). The hopper is preferably provided with at least one vibrator on its outer surface. The solid sulfur feed unit may also include a lump breaker crusher, depending on the form of sulfur to be melted. The solid sulfur feed conveyor is preferably provided with a cover arrangement in order to prevent contaminants from being deposited on the sulfur feed and to prevent sulfur dust from being emitted from the sulfur handling system. The high-capacity melting unit comprises a vessel made of steel or similar strong material, having a sloped bottom and provided with at least one mixer, or agitator, and at least one overflow pipe conduit. The vessel is sometimes referred to herein as the “melter”; and it is preferably substantially round with a contoured, or molded, sloped bottom, although it may also have a rectangular shape. The melter is also equipped with external steam blisters, spaced around its outer surface, and used to more conveniently control the temperature of the walls or surfaces of the vessel whenever the ambient temperature fluctuates and to maintain the vessel at the desired temperatures during shutdowns. The term “high-capacity”, as used herein in conjunction with the melting unit, refers to the fact that such melting unit is capable of melting sulfur at a rate of between about 200 and 5,000 tons per day (“TPD”), or higher. During normal operations in accordance with the method of the invention sulfur flows out continuously through the high-capacity melting unit overflow pipe conduit and into the compartmentalized pump tank assembly, and also simultaneously and continuously along the contoured sloped bottom of the melter, through the transfer pipe conduit(s) and into the compartmentalized pump tank assembly. The compartmentalized pump tank assembly is connected to the high-capacity melting unit and comprises (i) a collection compartment that is equipped to receive and hold molten sulfur from the melting unit, (ii) a pumping compartment located downstream from the collection compartment and equipped with pumps that pump molten sulfur to a shell-and-tube heat exchanger and to a molten sulfur product tank or other molten sulfur destination, (iii) a combination of a weir and a fine-mesh screen, both of which are located between the collection compartment and the pumping compartment, with the fine-mesh screen placed above the weir in such a manner that they cause large-size non-meltables (solids other than sulfur) to settle and be collected in the collection compartment, from where they may be conveniently removed periodically by an operator or by some other means, and (iv) steam blisters or similar means for providing sufficient heat to the compartmentalized pump tank assembly to maintain the temperature of the molten sulfur inside the assembly at approximately 245° F. or higher. At least one pump is provided in the pumping compartment of the compartmentalized pump tank assembly to pump and circulate molten sulfur through the shell-and-tube heat exchanger(s), and at least one pump is provided for pumping molten sulfur out of the system. Under certain circumstances it may be possible to have one pump perform both functions, that is, pump and circulate molten sulfur through the heat exchanger(s) and pump sulfur out of the system. The collection compartment allows the settling of the non-meltables in an area from where they may be conveniently removed periodically, as needed, for example by a mechanical excavator, thereby avoiding the significant delays encountered with conventional melting systems due to having to shut down the system for several days in order to allow time to cool and conduct a “turnaround”, i.e., to clean out the melter and pumping equipment, etc. 
         [0008]    Sulfur is pumped out of the pumping compartment located downstream from the collection compartment and sent to the prescribed shell-and-tube heat exchanger(s). The prescribed shell-and-tube heat exchanger(s) is (at least one) shell-and-tube heat exchanger designed so that some of the molten sulfur that accumulates in the compartmentalized pump tank assembly may be pumped into and flow inside the heat exchanger tubes while steam is made to flow inside the heat exchanger shell and allowed to condense on the outside of the tubes. Depending on the characteristics of the particular sulfur to be melted, other embodiments of the invention may also make use of different types of heat exchangers, such as plate-and-frame heat exchangers and others. In the shell-and-tube heat exchanger, or exchangers, enough steam is provided to heat the pumped molten sulfur in the heat exchanger tubes to a temperature of between about 275° F. and about 350° F. The heated molten sulfur is then made to exit the tubes of the shell-and-tube heat exchanger and flow into the high-capacity melting unit, where it releases the bulk of the heat (added in the shell-and-tube heat exchangers) to melt the incoming solid sulfur and maintain it in molten state. This feature of the melting system and method of the invention means that virtually all of the system&#39;s heating means required to melt the sulfur and maintain its temperature at between about 250° F. and about 300° F. are located outside the melting unit, and not inside the melting unit as is the case in most conventional sulfur melting systems and methods; in other words, the bulk of the heat transfer required by the unit operation takes place outside the melter and melting unit. A competitive advantage of the invention is that the system may be shop-fabricated as a plurality of modules, for example as a package of a bulk solid sulfur feed hopper module, a high-capacity melting unit module, a compartmentalized pump tank assembly module and a heat exchanger module, plus a conveyor assembly module. 
         [0009]    In one preferred embodiment of the invention a constantly flowing underflow arrangement is installed on the bottom of the melter&#39;s contoured, cone shaped bottom. This underflow arrangement provides continuous removal of non-meltable solids from the bottom of the melter and prevents their build up in the vessel, thereby greatly reducing the potential for significant delays encountered with conventional melting systems due to having to shut down the system for several days in order to allow time to cool and remove the built up solids from the bottom of the melting tank. By providing this underflow, the propensity for abrasion and other damage to the melter from constant movement of these particles is greatly reduced. A grating screen may also be installed as part of the arrangement to prevent very large particles from entering and plugging the underflow. 
         [0010]    In another embodiment of the invention a large, non-meltable trash collection sump is added to the bottom of the melter. The collection sump provides a location outside of the melter&#39;s vigorous agitation section where large non-meltables may collect. By providing this sump, the propensity for abrasion and other damage to the melter from constant movement of these larger particles is greatly reduced. A cleanout “man way” or “hand way” is normally provided to allow easy removal of these solids. A grating screen may also be installed in the sump when an underflow is provided as discussed above. 
         [0011]    In an alternative embodiment of the invention the system and the method disclosed herein are applied to and used in conjunction with a conventional sulfur melting unit of the type that incorporates and employs internal steam coils, or other heating means, located inside said conventional sulfur melting unit, to supplement and improve the efficiency of the sulfur melting operation. This may be done as a new design that combines the external heating concept of the present invention with the internal heating concept of conventional sulfur melting units; or it may be done by incorporating the external heating concept of the present invention to an already existing system that uses conventional internal steam coils, or other heating means, located inside the existing sulfur melting unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic diagram depicting the key components of the system of the invention arranged in the manner specified by one of the preferred embodiments of the system of the invention. 
           [0013]      FIG. 2  is a schematic diagram depicting the key features of the melter component (high-capacity melting unit) of a preferred embodiment of the system of the invention. 
           [0014]      FIG. 3  is a rendering of a modular sulfur melting system designed after one of the preferred embodiments of the invention and showing the key modular components of the system of the invention and the key unit operations of the method of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    By way of illustration, the sulfur melting system and the sulfur melting method of the invention will be described below with reference to one specific embodiment of the invention, specifically with reference to portions of a system that the owners of the invention have designed for a specific sulfur melting operation. It will be understood that a number of different embodiments are possible which may be adapted to suit the application of the invention to the particular circumstances of other sulfur melting operations. 
         [0016]    The specific system design of this particular embodiment is referred to herein as the “High-Capacity Sulfur Melter” or, simply, the “HiCap Sulfur Melter”. The HiCap Sulfur Melter is believed to incorporate the best melting technology in the industry, offering the lowest capital costs, the lowest operating costs and the highest operating efficiencies. In addition, it provides the lowest cost-per-ton of molten sulfur produced while operating within one of the safest methods of remelting sulfur. (Since sulfur is often melted, allowed to solidify and then melted again in many industrial operations, it is not uncommon in industry to use the term “remelting” and “remelted” interchangeably with “melting” and “melted”. No difference with respect to the physical process or unit operation of melting sulfur is intended herein between “melting” and “remelting”, or between “melted” and “remelted”.) The modular design of the HiCap Melters also lends itself to easy relocation and lower installation cost than melters used by other technologies. 
         [0017]    The specific HiCap Sulfur Melter system design of this particular embodiment has a rated capacity of 100 tons of sulfur per hour (“TPH”), i.e., 2,400 liquid tons of sulfur per day (“TPD”), and offers the following features and competitive advantages: (a) higher capacity allows much greater flexibility and lower cost for operations; (b) melting can be accomplished with reduced manning (reduced hours); and (c) melting rates may be increased or decreased as market conditions dictate and still accomplish the goal of timely melting the desired sulfur quantities. The specific HiCap Sulfur Melter system incorporates key design functionality, allowing lower maintenance costs, downtime and a high degree of automation. In addition, the modular design allows for easy relocation of the unit from block to block and minimizes installation manpower, cost and risk. 
         [0018]    The HiCap Sulfur Melter system comprises a combination of the following components: (a) a solid sulfur feed unit; (b) a high-capacity melting unit; (c) a compartmentalized pump tank assembly; and (d) a shell-and-tube heat exchanger located outside the high-capacity melting unit. These components are shown and identified on  FIG. 1 . Referring to  FIG. 1 , bulk solid sulfur  1  is fed at ambient temperature to solid sulfur feed unit  2  through bulk solid sulfur feed hopper  3  at a rate of approximately 100 TPH. Bulk solid sulfur feed hopper  3  is equipped with vibrator  4 , attached to its outer surface, and with lump breaker crusher  5 , attached to and below its cone shaped bottom. A grizzly  6  sits on top of hopper  3  and allows −10″ bulk sulfur to pass through and into vibrating hopper  3  and lump breaker crusher  5 , where its size is reduced to −2″. As used herein the designations −10″ and −2″ refer to those solid sulfur particles that have an average size of less than about 10 inches in diameter and less than about 2 inches in diameter, respectively. The −2″ bulk sulfur exits lump breaker crusher  5  and moves on to melter feed conveyor  7 , operably connected to the discharge end of lump breaker crusher  5 . Melter feed conveyor  7  is a variable speed belt conveyor comprising conveyor belt  8 , which is operated by rollers  9 , driven by conveyor motor  10 . It is convenient to maintain a stockpile of crushed vat sulfur or crushed lumps of sulfur nearby the solid sulfur feed hopper when melting. A front-end loader can be used to charge solid sulfur feed hopper  3  from the solid sulfur stockpile. 
         [0019]    The −2″ bulk sulfur  11  from melter feed conveyor  7  is fed to high-capacity melting unit  13  through conveyor discharge chute  12 . The rate of the feed (from hopper to melter) of −2″ bulk sulfur  11  into to high-capacity melting unit  13  is controlled by controlling the speed of conveyor belt  8 . The rate is normally determined by the heat that is available in the melter to melt the sulfur. Melter feed conveyor  7  is provided with appropriate instrumentation to help ensure its safe operation. 
         [0020]    Bulk solid sulfur  11  from conveyor discharge chute  12  enters the high-capacity melting unit vessel (also referred to as the “melter”)  14  and encounters hot liquid sulfur  44 , which is continuously fed to melter  14  from shell-and-tube heat exchangers  33  (as explained below) thereby forming a mixture of the two sulfurs (ambient-temperature bulk solid sulfur  11  and hot liquid sulfur  44 ). Melter  14  has an inner surface, an outer surface and a sloped bottom. The melter is preferably round or substantially round, with a contoured cone-shape bottom, and is preferably made of steel; however, it may have a rectangular shape or other shapes, and it may also be made of metal, such as stainless steel or aluminum, as well as of other strong material properly selected for operating at the previously stated temperatures. Melter  14  is equipped with at least one mixer, or agitator,  15 , driven by agitator motor  16 . Melter agitator  15  may create a vortex that immediately pulls the −2″ bulk solid sulfur  11  beneath the surface of the liquid sulfur, wetting all solid surfaces and thereby expediting the melting process. Simultaneously, the vigorous agitation immediately incorporates into the mixture hot liquid sulfur  44  (which is continuously fed to melter  14  from shell-and-tube heat exchangers  33 ), thereby providing rapid melting. One agitator with a single blade will suffice in many cases, but it is also feasible to use one agitator with multiple blades, as well as multiple agitators with single or with multiple blades. The temperature in melter  14 , i.e., the temperature of the inner surface and the outer surface of melter  14 , is maintained at approximately 245° F. or higher (and preferably between about 250° F. and 260° F., or higher) by the addition of liquid sulfur  44  heated in steam heated shell-and-tube heat exchanger(s)  33  to approximately between about 275° F. and 350° F. (and preferably between about 280° F. and 290° F.). The rate at which bulk sulfur  11  should be added to melter  14  is determined by the heat available for melting sulfur in melter  14 . The speed of conveyor belt  8  may be controlled by monitoring the temperature of the sulfur in melter  14  and maintaining the conveyor belt speed such that the temperature of the sulfur in melter  14  is kept at a constant pre-established level. In the HiCap Sulfur Melter system depicted in  FIG. 1  bulk sulfur  11  enters melter  14  at a rate of approximately 200 TPH; while hot liquid sulfur  44  from shell-and-tube heat exchanger  33  enters melter  14  at a rate of between about 400 and 800 TPH. 
         [0021]    Steam blisters  17  are provided on the outer surface of melter  14  to keep the outside surface and the inside surface of the melter hot enough (above approximately 245° F.) in order to conveniently prevent the sulfur in and around the melter from solidifying and clogging the vessels, pumps, conduits and other equipment during scheduled and unscheduled shutdowns (e.g., for cleaning, repairs, and/or regular maintenance) or for any other reason, including periodic fluctuations of the ambient temperature. The steam blisters do not contribute any significant amount of heat to the actual melting of the sulfur inside the melter, since all (or virtually all) of the heat used for melting the sulfur in the melter is provided by the molten liquid sulfur  44  that is generated in the shell-and-tube heat exchangers (as mentioned above and explained below). The steam blisters are preferably circular or semi-circular conduits equipped to receive 50 psig-steam from a steam source (not shown) and release condensate after giving off the required amount of heat. The blisters are preferably placed around and surrounding the melter vessel as shown on  FIG. 1  and  FIG. 2 . They also may have rectangular conduit shapes and may be placed around the melter in different configurations. In addition to or instead of the steam blisters other means may be used for providing sufficient heat to the melter to keep its outside surface and its inside surface above approximately 245° F. during scheduled and unscheduled shutdowns. Such other means include steam heating tracing, electrical heating tracing and heating devices that use hot oil or pressurized hot water, as well as other such heating means as may be available and practicable. 
         [0022]    Melter overflow molten sulfur  18  overflows and exits melter  14  by way of overflow pipe conduit  19  at approximately 255° F. and is directed to compartmentalized pump tank assembly  20 , where it first enters into collection compartment  21 . Likewise, limited rates of melter underflow molten sulfur  22  underflow and exit conical melter bottom  23  and are also directed to collection compartment  21  of compartmentalized pump tank assembly  20 . By directing underflow molten sulfur  22  into collection compartment  21  in this fashion the melting system is able to collect and eventually remove non-meltables  24  and prevent them from settling in the bottom of the melter. Non-meltable solids that are too large to pass through the underflow piping with underflow molten sulfur  22  are collected in trash sump  45 . These features, that is, the trash sump and directing underflow molten sulfur  22  into collection compartment  21 , extend the time between melter clean-outs, thereby improving the operability and the efficiency of the melting system and the melting method. Non-meltables include pebbles, rocks, nuts, bolts, bottles, pieces of wood, debris, plastic bags, plastic containers and the like, which tend to inadvertently enter the solid sulfur storage stockpile from time to time. In the HiCap Sulfur Melter system depicted in  FIG. 1  melter overflow molten sulfur  18  enters collection compartment  21  at a rate of between about 500 and 1,000 TPH; while melter underflow molten sulfur  22  enters collection compartment  21  at a rate of between about 30 and 60 TPH. 
         [0023]    Compartmentalized pump tank assembly  20  comprises a single tank that is divided into at least two compartments. The first compartment (collection compartment  21 ) is equipped to receive and hold molten sulfur from high-capacity melting unit  13 , and it is preferably subdivided into multiple sub-sections by means of one or more internal baffles  25 . The baffles provide a circuitous route for the molten sulfur flowing within compartmentalized pump tank assembly  20 , and thereby prevent or minimize short circuiting of the circulating molten sulfur to ensure adequate retention time in compartmentalized pump tank assembly  20 . Collection compartment  21  is also equipped with weir  26  and fine-mesh screen  27 , so structured and located that large-size non-meltables may be collected and caused to settle in collection compartment  21 , from where they may be conveniently removed periodically, as needed, by a mechanical excavator, or by some other practicable means, thereby avoiding having to shut down the system for several days in order to allow time to cool and conduct a “turnaround” (clean up the melter and pumping equipment, etc.). Weir  26  is made of steel, and typically would extend approximately 12 inches above the floor of compartmentalized pump tank assembly  20 , extending the entire width of the assembly, and welded or otherwise connected to both (opposite) sides of the assembly. Weir  26  may also be made of aluminum, stainless steel, plastic, synthetic or other strong material. Fine-mesh screen  27  is located contiguous with and above weir  26 , extending from the top of the weir to approximately 12 inches above the normal operating level of the molten sulfur in compartmentalized pump tank assembly  20 , and also extending the entire width of the assembly. Fine-mesh screen  27  is made of steel and has ¼ inch mesh openings. The screen may also be made of aluminum, stainless steel, plastic, synthetic or other strong material, and its mesh openings are typically anywhere between about 1/16 and ½ inch. For convenience in the maintenance and up-keep of the sulfur melting system fine-mesh screen  27  may be fabricated and installed as an easily removable and/or replaceable part of the system, and preferably would be designed to slide in and out of compartmentalized pump tank assembly  20  via a slotted guide. The design should preferably allow removal and replacement of the screen within the compartmentalized pump tank assembly in “hot” condition, i.e., while molten sulfur at 245° F., or higher, flows through it. 
         [0024]    Molten sulfur exiting melter  14  as melter overflow molten sulfur  18  and melter underflow molten sulfur  22  enters downstream collection compartment  21  and passes through fine-mesh screen  27  into pumping compartment  28 . Pumping compartment  28  is provided with pumps and pumping equipment that pump molten sulfur from compartmentalized pump tank assembly  20  to the shell-and-tube heat exchangers and to a molten sulfur product tank or other suitable destination. Thus, heat exchanger sulfur pump  29 , operated by heat exchanger sulfur pump motor  30 , pumps molten sulfur  31  into the tube side inlet head  32  of shell-and-tube heat exchanger  33 ; while product storage tank sulfur pump  34 , operated by product storage tank sulfur pump motor  35 , pumps molten sulfur  36  into sulfur product storage tank  39 . One or more strainers  37  are provided between compartmentalized pump tank assembly  20  and sulfur product storage tank  39  in order to remove certain entrained solid impurities that may still be present in the molten sulfur at this point in the system. Two duplex inline strainers are preferred for removing the entrained particulates. Clean molten sulfur product  38 , at a rate of approximately 200 TPH, is then stored in sulfur product storage tank  39 , from where it may be stored, pumped or otherwise delivered off battery limits to the customer&#39;s molten sulfur storage facilities. Sulfur product storage tank  39  is provided with steam blisters or other heating means (not shown) to aid in keeping it at an acceptable temperature. Depending on customer needs and the specific logistics of the operations, it may also be practicable to allow the sulfur in pumping compartment  28  to overflow pumping compartment  28  into another vessel or container rather than pumping it to sulfur product storage tank  39 . 
         [0025]    The bulk of the non-meltables that were caused to be deposited in collection compartment  21  can be removed from the bottom of compartmentalized pump tank assembly  20  in “hot” condition. When the volume of non-meltables builds up against weir  26  feed conveyor  7  is stopped and new bulk solid sulfur feed to the melting system is discontinued; a large hatch (not shown) on top of compartmentalized pump tank assembly  20  is then opened, allowing access to the interior of the assembly, where non-meltables  24  are subsequently easily removed by a few excavator scoops. Feed conveyor  7  is subsequently restarted and the melting process continued. This particular step (opening compartmentalized pump tank assembly  20  and scooping out accumulated non-meltables  24 ) only takes a couple of hours and is much faster and efficient than the steps taken in conventional melting methods, where tank cleanouts require drainage, cooling, clean out and reheating before resuming service, normally a five-to-seven day turnaround. Compartmentalized pump tank assembly  20  is provided with an automatic level control (not shown) such that all of the newly melted sulfur may be continually pumped to sulfur product storage tank  39  and, eventually, to customers&#39; liquid storage facilities. Compartmentalized pump tank assembly  20  is also provided with steam blisters  40 , or similar heating means, to aid in keeping it at an acceptable temperature (at least 245° F.). 
         [0026]    As explained above, heat exchanger sulfur pump  29 , operated by heat exchanger sulfur pump motor  30 , pumps molten sulfur  31 , at about 255° F., into the tube side inlet head  32  of shell-and-tube heat exchanger  33 , where the molten sulfur is heated to between about 280° F. and 300° F. and circulated to high-capacity melting unit  13 . More than one pump may be used to pump molten sulfur  31 . The pump, or pumps, should provide sufficient pressure to pump the molten sulfur through the heat exchanger tubes and allow it to reach melter  14  after being heated to the desired temperature (between about 280° F. and 300° F.). In a preferred embodiment two shell-and-tube heat exchangers, connected in parallel, are used to perform the function of shell-and-tube heat exchanger  33 . Steam  41  is injected into shell section  42  of shell-and-tube heat exchanger  33 , where it give off heat before condensing and exiting shell-and-tube heat exchanger  33  as condensate  43 . Maintaining steam pressure on the shell side of the exchanger at about 70 psig (316° F.) maximizes heat transfer without tube fouling. Flow rates through shell-and-tube heat exchanger  33  are designed to maintain satisfactory heat transfer coefficients and prevent tube fouling. In this fashion virtually the entire source of the heat supplied to high-capacity melting unit  13  for melting sulfur is provided by high-efficiency shell-and-tube heat exchanger  33 . The thus heated molten sulfur exits heat exchanger  33  as hot liquid sulfur  44 , at between about 280° F. and 300° F., and is then circulated to melter  14 , where it transfers its heat to incoming bulk solid sulfur  11 . 
         [0027]    A molten sulfur product destination may be a sulfur product tank, similar to sulfur product storage tank  39 , or it may be a sulfur processing system such as a sulfur filtration unit or any other system commonly employed to further process molten sulfur for a number of industrial uses, such as for feed to sulfuric acid manufacturing plants and the like. In order to achieve high efficiencies in the operation of the melting system and method the degree of turbulence provided inside the shell-and-tube heat exchangers should be enough to cause good heat transfer, but not so much as to cause erosion (excessive wear) of the tubes; also the amount, temperature and pressure of the steam used and the flow rates of the molten sulfur streams should be monitored and controlled in order to maintain the prescribed temperature ranges in the melter and in the shell-and-tube heat exchangers. 
         [0028]    A preferred embodiment of the high-capacity melting unit of the invention is shown in  FIG. 2 , where melter  51 , equipped to receive solid sulfur through sulfur feed inlet pipe conduit  52  and molten sulfur through molten sulfur inlet pipe conduit  53 , is depicted with one single agitator  54 , having a single blade  55  and driven by agitator motor  56 . Melter  51  is also provided with sulfur overflow pipe conduit  57 , baffles  58  and steam blisters  59 . The steam blisters are welded to the outer surface of melter  51 , including the outer surface of its conical sloped bottom  63 . Agitator  54  is used to provide vigorous agitation of the mixture of solid sulfur coming into the melter through sulfur feed inlet pipe conduit  52  and hot molten sulfur coming in through molten sulfur inlet pipe conduit  53 . The vigorous agitation of the mixture immediately pulls the incoming solid sulfur beneath the surface of the liquid sulfur, wetting its solid surface and also quickly incorporating into the mixture the incoming hot molten sulfur, thereby causing the rapid melting of the incoming solid sulfur. Baffles  58  prevent the mixture from just spinning inside the melter; and the impact of the moving molten sulfur hitting the baffles causes additional turbulence and mixing within the melting unit. Baffles  58  also cause the molten sulfur to sweep across melter conical bottom  63 , thereby reducing the potential for settling and buildup of non-meltables on the bottom. A first portion of the molten sulfur exits melter  51  through sulfur overflow pipe conduit  57  and is directed to the compartmentalized pump tank assembly of the system. A second portion of the molten sulfur passes through trash sump  61 , exits the melter through sulfur underflow pipe conduit  60  and is also directed to the compartmentalized pump tank assembly of the system. Non-meltable solids that are too large to pass through sulfur underflow pipe conduit  60  are collected in the upper portion  66  of trash sump  61  from where they may be periodically removed through trash sump access man way  62 . Removal of these larger solid non-meltables may be conveniently done by opening the blind closing flange of access man way  62  and disposing of them in appropriate fashion. Non-meltables include pebbles, rocks, nuts, bolts, bottles, wrenches, bricks, pieces of wood, debris, plastic bags, plastic containers and the like. Grating screen  64  separates upper portion  66  of trash sump  61  from the lower portion  65  of the sump. Non-meltables generally gravitate towards conical slopped bottom  63  of melter  51  and find their way into trash sump  61 . Sulfur in trash sump  61  is generally outside of the vigorous agitation that takes place in melter  51  which allows both the larger and the smaller non-meltables to accumulate there. As previously mentioned, the larger non-meltables accumulate on the upper side of grating screen  64  in the upper portion  66  of trash sump  61 , while the smaller non-meltables travel through grating screen  64  and into lower portion  65  of trash sump  61 . The smaller non-meltables then travel with the aforementioned second portion of the molten sulfur which is passing through trash sump  61  and, together, they exit melter  51  through sulfur underflow pipe conduit  60 , and are further directed to the compartmentalized pump tank assembly of the system, as shown on  FIG. 1 , where they are made to settle out and from where they are periodically removed by an excavator bucket or similar means. 
         [0029]      FIG. 3  depicts the sulfur melting system of the invention in modular form, showing the key shop-fabricated modular components of the system and the key unit operations of the method of the invention. Referring to  FIG. 3 , melter  71  is equipped with solid sulfur inlet  72 , adapted to receive solid sulfur from a conveyor discharge chute of a solid sulfur feed unit (not shown). Melter  71  is also equipped with steam blisters  73 , spaced around its outer surface, and with sulfur overflow pipe conduit  74 . Molten sulfur from melter  71  is made to flow through sulfur overflow pipe conduit  74  into collection compartment  75  of compartmentalized pump tank assembly  76 , which is equipped with steam blisters  77  to aid in providing sufficient heat to keep the molten sulfur that flows through the assembly at the desired temperature of at least 245° F., as already explained. An excavator  78  is shown scooping out non-meltables from the bottom of compartmentalized pump tank assembly  76 . Hatch  85 , on top of compartmentalized pump tank assembly  76 , provides access to the interior of the assembly, where the non-meltables are easily removed by a few excavator scoops. Heat exchanger pump motors  79  operate the heat exchanger pumps that pump molten sulfur out of compartmentalized pump tank assembly  76  through sulfur pipe conduits  80  into shell-and-tube heat exchangers  81 , arranged in parallel fashion. Product sulfur pump motor  83  operates the product sulfur transfer pump that pumps molten sulfur out of compartmentalized pump tank assembly  76  through sulfur pipe conduit  84  into a sulfur product storage tank (not shown). The heated molten sulfur exits the tubes of shell-and-tube heat exchangers  81  through sulfur pipe conduits  82  and flows into the upper portion of melter  71 , where it releases the bulk of the heat added in the heat exchangers, thereby melting the incoming solid sulfur fed to the melter through solid sulfur inlet  72  and maintaining it in molten state, thus completing the unit operation cycle. 
         [0030]    Routine maintenance of the sulfur melting system by the operators may consist of general house-keeping, the switching and cleaning of operating strainers as their elements begin to clog and normal maintenance of lubricants, tightening valve packing, repair of minor steam/water drips, etc. Scheduled turnarounds may include pump, agitator and general conveyor servicing and routine motor control center maintenance, which can be done on a periodic basis. If convenient, the compartmentalized pump tank assembly may receive a complete cleanout during turnarounds. 
         [0031]    While the present invention has been described herein in terms of particular embodiments and applications, in both summarized and detailed forms, it is not intended that any of these descriptions in any way should limit its scope to any such embodiments and applications; and it will be understood that substitutions, changes and variations in the described embodiments, applications and details of the method and the formulations disclosed herein can be made by those skilled in the art without departing from the spirit of this invention. 
         [0032]    Where the article “a” (or “an”) is used in the following claims, it is intended to mean “at least one” unless clearly indicated otherwise.