Feature
“Quick Fit” pre-assembled acid-proof lined equipment By: Roland Günther and Oliver Schmidt, Senior Project Managers, Export Sales STEULER-KCH GmbH
The following case study describes the production of a large steel vessel with rubber and brick lining in a Steuler shop and delivering it to the customer site to minimize the shutdown period and reduce the costs of onsite mobilization and loss of production.
Scope of work / job definition / inquiry
A nonferrous metal winning plant in Europe requested to renew its more than 25-year old existing Venturi scrubber in the gas cleaning unit that cleans the off gases after the ore roaster. Not only the brick lining and the membrane had to be replaced, but also the steel shell. Other considerations were that the repair had to be completed during a short 10-day shutdown period and the new Venturi scrubber had to fit into the existing steel frame. Also, the narrow and complicated plant layout made it difficult to maneuver a big crane that was required to lift out the existing Venturi scrubber and lift in the new one. Additionally, the client facility had no place next to the existing Venturi scrubber to erect the new one and the only possibility was to line the new one 200 meters away from the job site.
Solution
After evaluating all the given parameters, the Steuler team determined that the best way to replace the Venturi scrubber within the short period of ten days was to send a new rubber lined and brick lined Venturi scrubber to the site, lift the old one out and put the new one in.
Execution of work
According to the dimensions of the existing Venturi scrubber, the Steuler team prepared a new steel drawing which incorporated the statistical calculations as well as the details of the brick lining, as shown in Fig. 1. Total weight of the Venturi scrubber was 31.5 tons. The team took special care to ensure that the connections to the existing gas duct, spray nozzles and lower part of the Venturi scrubber fit the existing onsite
Fig. 1: Drawing of the new Venturi scrubber.
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Fig. 2: Autoclave dimensions: diameter of 6 m and length of 15.3 m.
equipment. Also, the team constructed the necessary lifting lugs for transportation and lifting on site. For the scrubber’s membrane, the team used Steuler’s own graphite-filled hard rubber lining, Vulcoferran 2190, thickness 4 mm, with excellent chemical and diffusion resistance and a maximum service temperature of 100 degrees C. Vulcoferran is based on natural rubber (NR) and is vulcanized in an autoclave. The rubber lining produced in the shop and the vulcanization in the autoclave ensures a definite universal high quality with minimum risk of failure. Steuler’s autoclave can accommodate vessel sizes as large as 5.8 m in diameter by 15 m long. See Fig. 2. After the vulcanization and quality assurance test for the rubber lining, e.g. thickness, hardness, spark test etc., the Venturi scrubber was transported to the brick lining workshop, where the installation of the brick lining was completed. In order to avoid exposing the rubber lining membrane to temperatures higher than 80 degrees C in operation, the team constructed the thickness of the brick lining according to a thermal heat calculation, as shown in Fig. 3. During construction, holes were drilled for the 4 tangential spray nozzles with a special drilling machine. This was done in this way because there are very critical areas where the bricks are very small and thin,
Fig. 3: Thermal heat calculation.
Fig. 4: Drilling nozzle openings.
Fig. 5: Drilled nozzle opening in inner layer of nitride bonded silicon carbide bricks.
and cutting them would be very difficult. Drilling ensures that the openings for the spray nozzles are in the correct orientation and that the brick lining is made without cavities. With regard to the drilling, see Fig. 4 and Fig. 5. During the brick lining construction, Steuler’s experienced fitters maintained defined temperatures in the workshop. The bricks and mortars were selected to withstand chemical attack as well as mechanical and thermal shock stress. Fig. 6 shows the construction of a typical brick lining in a Venturi scrubber. After finishing the brick lining work and a hardening time of six days, the team and client together made the final acceptance and closed all nozzles with wood or plastic. On the upper gas inlet flange, the team installed a 20 mm thick counter flange which was required on site and also made the vessel stiff and inflexible for transport and lifting. That prevented damage during the transport via truck to the site through three countries as well as lifting to the final position. Upon the client’s request, Steuler delivered the Venturi scrubber just in time to the site on a special air sprung flatbed truck. The lifting out of the existing Venturi scrubber and the lifting in of the new one, performed by a client subcontractor but supervised by Steuler, was completed in a very short time (see Fig. 7). After all nozzles and ducts were connected to the plant, Steuler made the final inspection together with the customer to ensure that no damages had occurred during the transport, lifting and connection work. Sulfuric Acid Today • Spring/Summer 2016