Cellhouse, cost

The electrical supply equipment is the second biggest equipment package after the mechanical equipment. The package includes the transformer/rectifier (T/R) sets and bus bars for providing DC power to the cells, the associated power factor correction equipment and harmonics filtration equipment, and the service transformers and circuitry. This equipment will typically comprise about 15 - 25 % of the cellhouse cost. The cost is heavily influenced by whether or not an electrical substation is included, and by the redundancy requirements for the T/R sets. A plant can choose to have no spare T/R capacity, partial redundancy, or full redundancy. Such cost savings must be weighed against the cost of lost production when a T/R set fails. 

In 1997, the Hikoshima smelter carried out an expansion of the cellhouse, which then was the bottle neck of production, and increased its production fiom 59,200 t/y to 71,000 t/y. The major features of this expansion project were increasing the number of cells, increasing the working efficiency of the cells and raising the current density. We plan to cany out further improvements, such as anode maintenance while energizing the cells, to establish ourselves as a cost competitive smelter in the world. 

The lijima Zinc Refinery is being challenged to become more profitable by recovering all by-products, such as Au, Ag, Cu, Pb, rare metals, iron oxide and so on. An increase in zinc production caused an increase in these metals as well. Simultaneously, the fixed cost decreased significantly with an expansion and cellhouse automation. We achieved one of the most competitive costs in the world. 

We will instead discuss the issues beyond the design of the mechanical and process equipment, which can have significant effects on capital and operating costs. Some important differences between a greenfield and brownfield project are presented, followed by key considerations during site selection. The major components of capital cost are discussed, with emphasis on electrical power and the design of the cellhouse building. Finally, the factors that affect the project schedule are discussed. 

The motivations for replacement of an old cellhouse are nearly always the same reduce manpower for manual cathode stripping, improve workplace conditions for the employees, and reduce power costs. The need to expand capacity or improve product purity can be factors as well. It is also frequently the case that an old manually stripped cellhouse has high maintenance costs and may need major repairs to stay in operation. 

In a brownfield site, the conditions can be much more challenging. An old plant that has been modified and expanded over the years has probably already used up the best building sites. The new cellhouse could have to face the costs of building on inferior ground. Conditions that can render the ground inferior are ... 

Outside of the plant boimdaries, the security of the power supply must be reviewed, hi co-operation with the power provider, redimdant power sources, substations and transmission lines should be examined carefully and various scenarios analyzed for costs and benefits. Ideally, upgrading costs should be shared among all the beneficiaries of the upgrading. There is a danger, however, that the upgrading cost will be borne by the cellhouse project, either directly or indirectly. In the absence of a users agreement, this becomes more likely. 

Table I - Major Cellhouse Building Decision Checklist Major Cellhouse Building Decisions That Can Impact on the Cost and Schedule of a Project...

Will the cells sit on ground slab or will there be a basement The placement of electrolytic cells on the ground, slightly off the ground, or with a full hei t basement underneath has a significant impact on the building cost and the operational philosophy of the cellhouse. 

Relative cost of cellhouse building 109% Smaller members, giving larger working area... 

Table HI - Relative Costs for Three Cellhouse Building Options (Case 2)...

Table IV - Fundamental Zinc Cellhouse Design Criteria that Impact on Building Cost...

The sentiment of the design team was to avoid using option 3, the cathode insulator disk, because of the additional development effort required to implement this technique, and the cost of conversion of all 26,400 cathodes in the cellhouse. 

Another series of 24 tests was conducted under continuous operation aiming to determine whether it was possible to obtain good Faradic performance and a smooth morphology by operating the cellhouse at a current density of 1,200 A/m. Operating at such a high current density is vital to the viability of the process since electrolysis costs would account for a major part of a refinery project. The study was carried in two phases ... 

Cell fi eeboard is the distance from the electrolyte level to the top of the cell. The first designs of EW cells had large freeboards, typically of 300 mm or more, but in more recent cellhouse designs, this was reduced to around 150 mm to save costs. A potential opportunity for investigation exists to review freeboard impact on acid mist above the cells. 

---