Figure 3 A plate-based MBHE illustrating how the product enters the unit from the top and flows by gravity through vertically orientated banks of stainless steel pillow plates ( Source: Solex Thermal Science)
their inherent safety redundancies. When conventional CHEs fail, entire systems must be taken offline to avoid
contamination or mixing of process streams. Conversely, an HPHE can continue operating safely even in the rare instance that a heat pipe fails since process streams remain isolated. During scheduled maintenance, failed heat pipes can be
heat transfer efficiency. Both MBHE types are also equipped with a mass flow discharge feeder controlling the flow rate through the unit. Gravity facilitates the slow movement of the product through the heat exchanger. Beyond heat transfer efficiency, this technology gently handles the product, minimising fugitive dust emissions and degradation while ensuring a consistent and uniform temperature of the granular material exiting the heat exchanger. These advantages are crucial for many downstream processes. Heat transferred from the granular solids to the working fluid can be utilised elsewhere to reduce overall energy costs. For example, in metal refineries and mineral processing facilities, MBHEs can be used to cool material downstream of kilns while reducing dust emissions. Then, the hot working fluid produced from the cooling process can provide thermal energy for use elsewhere in the plant – for example, upstream in the production process to preheat combustion air feeding steam boilers. In low-temperature applications, MBHEs can be uniquely combined with industrial heat pumps to upcycle energy from waste to a heat source. By adding a heat pump, the temperature of a cooling water stream can be increased to levels that are useful to plant operators. Temperatures between 110°C and 150°C are easily achievable, with the ability to reach around 180°C in some cases. Further, since heat pumps are electrically driven, they do not create any additional direct emissions. Case studies The following examples demonstrate how the technologies described above are playing respective roles in minimising energy consumption and reducing emissions. Case study 1: Oil refinery air preheater Oil and gas refineries often encounter issues with traditional air preheaters due to flue gas
easily identified, isolated, and replaced without disassembling the whole unit. Moving bed heat exchangers (MBHE) Combustion gas streams are not the only source of valuable and potentially wasted heat generated from industrial processes. Every year, vast quantities of free-flowing bulk materials are processed to produce a wide array of products, with many of these processes bearing a high carbon footprint. For example, the cement industry alone accounts for approximately 7% of global greenhouse gas emissions annually. MBHEs provide another opportunity for heat integration. They efficiently transfer energy to and from free-flowing solid materials with minimal energy requirements and a low environmental impact. In either a vertical plate or vertical tube orientation, MBHEs exchange heat between granular solids and a heat transfer fluid through conduction. This method differs from convective heat transfer techniques used in less efficient, direct-contact solutions such as fluid beds and rotary drums. When using plate-based MBHEs, primarily for solid-to-liquid heat transfer, the product enters the unit and flows by gravity through vertically orientated banks of stainless steel pillow plates (see Figure 3 ). A heat transfer fluid passes through the plates, cooling the material as it descends. When using tube-based MBHEs, mainly for solid-to-gas heat transfer, solids flow by gravity through vertically orientated tubes while gas (such as air) flows outside the tubes. Both types of MBHEs commonly use a counter- current flow arrangement between the product bed and heat transfer fluid, intended to maximise
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