Process Equipment Update


4 Sean Ottewell reports on the latest high-pressure spiral heat exchangers, plate heat exchangers and brazed plate heat exchangers that are designed to reduce fouling and cut corrosion – two major problems for process operators.


Fouling and corrosion tackled by new heat exchangers


its new high-pressure spiral heat exchangers (HPSHEs). These are high-pressure versions of the company’s existing SHEs with a design pressure of 100 barg and what the company describes as a highly efficient, self-cleaning effect. True process heat exchangers, they can replace shell-and-tube units (S&Ts) in sensitive processes, eliminate fouling problems and offer a high level of heat recovery. Fabrizio Palmeri, manager, market unit refinery,


A


Alfa Laval, says: “An HPSHE continuously recovers maximum heat energy from bottom residues, while its single channel geometry gives it an ultra-efficient self-cleaning effect that prevents it from fouling. The HPSHE’s capability to withstand pressures of up to 100 bar and high temperatures makes it an efficient process heat exchanger for visbreaking, fluid catalytic cracking, desalting, coking and other processes. Although compact, it offers two to three times higher heat transfer efficiency than an S&T unit.” An S&T unit


normally requires cleaning several times a year. An HPSHE only requires servicing every four to five years and can be cleaned easily by backflushing,


hydroblasting, or in-line chemical cleaning. HPSHEs interiors are accessed


by means of an easily opened front cover.


Fig. 1. An HPSHE requires minimal servicing and is easily accessed. Picture courtesy Alfa Laval.


16 www.engineerlive.com


This gives them a small service footprint, unlike S&Ts where space must be allowed for long tube


problem that causes continuous concern for many process companies is fouling of heat transfer equipment. Alfa Laval has risen to this challenge with


bundles to be withdrawn and cleaned manually (Fig.1).


“Since the heat recovery performance of an


HPSHE will not be reduced by fouling, extra process heat will not be required from the furnace,” says Palmeri. “This cuts fuel costs and reduces carbon dioxide emissions.” HPSHEs consume only a quarter of the


pumping energy required by S&Ts. Also, as there should be no fouling to increase the pressure drop over the heat exchangers, no extra pumping energy will be needed either. This means substantial energy savings.


Cleaner wastewater


In Sweden, Örebro-based EON for many years has employed a policy of re-using purified wastewater. Wastewater is pumped from a pumping station in Skebäck up to two heating pumps at the Åbyverket CHP plant, where heat is recovered from the cleaned wastewater. Once that process is complete, the now cooled wastewater is pumped back via Skebäck and released into the river Svartån which flows into Lake Hjälmaren. In 1998, EON also began supplying district


cooling to Örebro University Hospital, Örebro County Council and international paper and packaging company Mondi. As by definition the wastewater is not clean, it has to be purified. This meant that EON had to invest significant time and resources on site to clean customers’ heat exchangers. This was viewed as an unnecessary cost by both customers and the supplier. When EON was awarded the contract to supply


district cooling to central Örebro, the decision was taken to build a dedicated heat exchange station adjacent to the pumping station in Skebäck. Wastewater is now exchanged via a clean water system that is then distributed to the Åbyverket plant and sent on to district cooling customers. .


Cooling water


Tranter has supplied two GXD-205 gasketed plate heat exchangers to exchange between purified wastewater and district cooling water. Total output is 18MW, 9MW per heat exchanger. Tranter’s plate heat exchangers are ideal for applications with close temperature approach. For this particular application, the heat


exchangers were designed with one bar pressure


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