Thhe Challlenge off Addinng Cooliing Capaacity to an Exissting Ferrtilizer Plant
Ms. Ma arietta M Mansve elt So olex The ermal S Science e Inc. Canad da
The Challenge of Adding Cooling Capacity to an Existing Fertilizer Plant Many fertilizer facilities in the course of their lifecycle will require expansion for the purpose of increasing capacity. Increasing total capacity to a facility requires adding additional cooling capacity to cool the fertilizer in the final stages of production. Ensuring sufficient cooling capacity is important because it reduces the likelihood of caking and lumping of the fertilizer. Increasing cooling capacity can be a significant challenge for two reasons. Older facilities have typically been built using fluid bed coolers for the final stage of fertilizer cooling. In order to increase cooling capacity, another fluid bed cooler must be added. The first obstacle to adding another cooler is the physical size of the cooler itself. The second challenge is the increase in air emissions created by the added cooler. Solving these two problems is not easy since the existing facility has two constraints that compound the problem. Firstly, existing facilities are limited in physical space (see figure 1) in which to add an additional fluid bed cooler. Fluid bed coolers are designed to be installed horizontally and therefore require a very large installation footprint. A typical fluid bed cooler footprint in a 100 t/h plant is 3m wide x 8m long. Accommodating the additional equipment is not only a challenge, but any possible solution will be costly. Secondly, fluid bed coolers rely on massive amounts of air in order to achieve the required cooling. A fluid bed cooler in a typical 100 t/h fertilizer plant will require approximately 350 – 400,000 Nm3/hr of chilled air. This additional air capacity must somehow be treated; however, existing scrubbers, filters and bag houses are unlikely to be sized to accommodate such additional volumes of air. As a result, additional scrubber capacity must be added to the facility to enable the installation of the added fluid bed cooler. Adding such additional filters, ducting, and scrubbers to an existing facility is difficult, expensive and can also require the added burden of dealing with emissions permits.
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The Real Challenge Until now, there have been few technology options available that work well for cooling fertilizer. As a result, the industry settled on fluid bed coolers as the standard. But clearly, in the case of capacity increases, a better option is needed. The ideal solution that would enable additional cooling capacity to an existing fertilizer plant would be a technology with a small footprint that does not rely on additional air volume for the cooling process. The Benefits of Indirect Plate Cooling Technology Advancements in indirect plate cooling technology and experiences from many successful installations are proving that the benefits of this technology for fertilizer cooling applications are too important to ignore. The main benefits for fertilizer plant expansions are the fact that this technology completely eliminates the footprint and air emissions issues experienced with fluid bed coolers. As a result, this technology is being quickly adopted as the logical solution in such applications. About Indirect Plate Cooling Technology – How It Works The heart of the indirect plate cooling technology is the bank of exchanger plates, installed vertically inside the heat exchanger housing. The product to be cooled flows slowly downward between the plates. Cooling water flows through the plates in counter flow and the product is cooled by conduction. Mass flow of the product is achieved by means of a Discharge Feeder mounted as an integral part of the exchanger below the plate bank. The Discharge Feeder also regulates the flow of product through the exchanger to keep it full at all times. A 3D view of a Bulk Solids Cooler is shown in Figure 1.
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Figure 1
The indirect cooling technology cools the fertilizer indirectly with water. The unique advantage of this technology is the indirect method of cooling and the fact that air is not used in the cooling process. What Are the Implications of Cooling Without Air? With indirect cooling, the cooling fluid is plant cooling tower water. This has the big advantage that the thermal cooling duty is “free,” except for the cooling water pumps. In comparison, a fluid bed cooler requires large volumes of chilled air. Chilling the air is very energy inefficient because the heat load includes the heat to condense the water out of the air to the dew point. Furthermore the air has to be “over‐cooled” and then reheated so that it is not saturated when it enters the cooler. With indirect cooling, the cooling media does not come into direct contact with the product, which means no dust or emissions are created. This eliminates the problem of having to add more pollution control equipment associated with fluid bed coolers. The amount of work and the cost of the installation of the additional cooling equipment are thereby greatly reduced. It also means that the addition of cooling capacity does not add to emissions permitting concerns. 283
The Benefits of a Vertical and Modular Design The nature of the indirect plate cooling technology is the vertical configuration. This design means that the installation footprint of the indirect plate cooler is approximately 85% less than that of a fluid bed cooler. The installation footprint of a typical fluid bed cooler in a 100 t/h facility is 3m x 8m. The equivalent indirect plate cooler is only 1.6m x 2.4m—a fraction of the size. The compact installation footprint means that the space required to add additional cooling capacity to an existing facility is greatly reduced. Not only is adding cooling capacity now feasible, the costs are greatly minimized and the time required for installation significantly reduced. There is one more important benefit of the vertical design that is unique to this indirect plate cooling technology. Since the plate banks are installed vertically inside the heat exchanger housing, it is possible to add more heat exchanger plate banks in the future if more cooling capacity is required. See figure 2. Capacity increases with the indirect plate cooling technology are a manageable task compared to the addition of an entire new fluid bed cooler. In fact, new facilities that start out with indirect plate cooling technology find that adding more cooling capacity does not present any of the common issues associated with attempting to add capacity using fluid bed coolers. 284
Figure 2
What About Efficiency? The indirect plate cooling technology offers significant benefits that enable the addition of cooling capacity in fertilizer expansions and helps reduce the costs and workload in doing so. However, once installed, what are the operating costs of the indirect plate cooling technology compared to fluid bed technology? The question of efficiency is important. The premise behind fluid bed cooling technology is that large volumes of chilled air are used to both fluidize the material (required to enable the product to flow) and to act as the heat exchange medium—adding or removing heat from the process. With this technology, ambient air is taken in using large fans and, in most climates, the air must be chilled before blown across the product using large horsepower fans. The air leaving the fluid bed cooler is then discharged through an emissions stack. Both the chilling process and the circulating fans have high energy requirements. 285
By comparison, indirect plate cooling technology works by cooling bulk solids indirectly using water. No air is used in the cooling process. With this technology, cooling water is pumped through a vertical bank of hollow stainless steel plates while the bulk solid passes between the plates with sufficient residence time to achieve the required cooling. The inherent problem with using air to directly cool fertilizer is the large quantity of air required and the expense involved in chilling, processing and cleaning that air. Below is an energy comparison between a fluid bed cooler and the indirect plate cooling technology. As can be seen, the indirect plate cooling technology uses up to 90% less energy than fluid bed technology. Indirect Plate Cooling Technology Uses up to 90% Less Energy
Conclusion Advancements in indirect plate cooling technology make it an ideal solution for fertilizer expansions and debottlenecking projects because of its compact installation footprint, ability to cool without air and its ultra high efficiencies. The modular design makes it possible to add more cooling capacity with relative ease and will make it a logical choice not just for expansions but also for new facilities in the future. 286