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Chemical Industry Case Study

CHROME EVAPORATOR DEVELOPMENT

Electroplating solutions, such as chromium plating produces lot of heat during plating, which raises the temperature of the plating tank above the acceptable limits. This solution must be cooled down to produce acceptable deposits at optimum temperature. The heat released in the plating process, which otherwise is wasted, can be utilised to supply heat energy required for recovered chrome solution evaporation thus resulting in a lot of energy being saved.

 

The chromic acid recovered from the chrome recovery system has to be of a certain concentration before it can be added into the main plating tank. For this, a chrome evaporator is used as it is most energy efficient. It operates using the principle of evaporation where the hot solution is sprayed from the top of the column and drops down through a packed column in the reservoir tank. Air is blown from the bottom & a chamber gets saturated with water vapour. A demister is provided to separate any droplets from the air.

(Fig 1)

Objective

Fabwell sought to design and develop a new version of the chrome evaporator assembly that would last much longer than its predecessor (i.e. from 4 years to 6 - 8 years) , by using a combination of mild stainless steel for the outer casing or main body, and a material called Niobium for the inner liner. Niobium is a highly ductile, soft refractory metal that is seldom used in manufacturing.

The technological baseline and status at the start of the project

The existing chrome evaporator (fig 2) was not suitable in as much as it was not sufficiently durable and often leaked during operation. The evaporator had been created by a company based overseas and the design was poor. Hence, with no off-the-shelf solution readily available to resolve the issues faced, a bespoke development programme was required.

(Fig 2 - Old Chrome Evaporator Vessel)

Work done

The project commenced with a feasibility study where Fabwell sought to understand how the chrome evaporator functioned as well as its size, dimensions and the space constraints; the issues with the current version and the operating conditions; the properties and behaviour of materials that would be used on the new version etc., before a suitable design, development and implementation strategy could be identified (BEIS guidelines paragraphs 27b, 31g and 36).

 

Using the knowledge acquired as a foundation and following a critical assessment, a technical scoping exercise was conducted for creating the components of the chrome evaporator together with a detailed project plan for monitoring progress and task execution at each stage. Fabwell subsequently undertook an iterative design exercise using CAD software, exploring a number of design configurations for the parts that were needed. Furthermore, special support jigs were designed and machined to support manufacture.

 

A number of CNC machining strategies were explored to determine the most ideal tool paths, material feeds and speeds. In parallel, potential methods to weld the two different materials as effectively as possible were explored with arc welding being chosen as the best option. Furthermore, a suitable method of stress relieving each of the components post machining was conducted as it was imperative that any stresses induced during manufacture were removed, to achieve structural stability on assembly with no warping or distortion. Special troughs were developed around the welded joint to minimise the effect of oxidation on the welds. Photos of the new chrome evaporator are shown below while drawings of the parts can be found in appendix 2.

(Fig 3)

Testing

Fabwell conducted a rigorous in-house testing and validation process to prove out the principle of operation and ensure the new chrome evaporator assembly met the desired technical specification with regards to its size, weight, fit, form, performance, robustness, durability and ease of assembly. The dimensions of the evaporator were first verified on a CMM. This was followed by dye penetration inspection of the welds as well as pressure and leaking testing (BEIS guidelines paragraphs 27c and 39). All tests met the standards and the crome evaporator was put into service.