Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 41

The activities presented in this book, some of it in this chapter as part of the electrical design, include the following:

 Determine the site conditions and discuss the interconnection with local Utility.

 Review of mechanical load flow diagrams, P&D diagrams and establish load (kW) estimates and voltage levels.

 Prepare one‐line diagrams and plant design criteria.

 Conduct system studies and determine electrical equipment ratings.

As the starting point, the mechanical engineers will develop 10–20 flow diagrams of the plant process. A small part of the ore handling flow diagram is shown in Figure 2.2. The process (instrumentation) engineers will develop 30–40 process piping and instrumentation diagrams (P&ID) to instrument and automate the plant, as shown on a small P&ID segment in Figure 2.3 for a feed pump. The P&ID gives us the indications on how the plant will be controlled, monitored, and operated.

Figure 2.2 Part of plant flow diagram.

Figure 2.3 A part of a P&ID diagram.

As a young design electrical engineer you have been assigned to be a part of a multidiscipline engineering team responsible to develop a project estimated to consume about 30 MW of power, or 37.5 MVA at 0.8 power factor (pf). The design team of electrical engineers and draftsmen led by an experienced senior lead electrical engineer is responsible to design the electrical power distribution system and procure the electrical equipment to power up and control the plant equipment. The plant distribution system will follow the national standards and voltages for 60 Hz (50 Hz) frequency as applicable to the location of the project.

The principal operating item in this facility and the biggest electrical load is a large 10 MVA semi autogenous grinding (SAG) mill operated as a variable speed drive cyclo‐converter. It receives the ore from the crushers, as 10–20 cm chunks of raw material and reduces it to 1–2 cm large gravel. The mill speed is regulated in accordance with the hardness of the ore, which may vary on a daily basis. This material is then conveyed to ball mills, which pulverize the product to allow it to be mixed with water and pumped around as slurry through the rest of the plant. The slurry will be then subjected to some chemical treatment processes to separate the metal from the ore.

What is the operating basis for this project? The owner will look at operating the plant 24 hours a day to maximize his early output in order to quickly pay off the loan to the financial institution. The only way to do that is to run the facility around the clock in two 12‐hour shifts. This operating regime is also favored by the local utility, as it allows them to run more generation around the clock as less costly base load and flatten the load cycle.

A housing complex for 100 people will be built at a site about 3 km away from the main process plant for the workers to build and operate the plant. This is an area away from the plant crushers. Operators are happy to work long shifts seven days a week on a basis of three weeks in and one week out. The housing complex (camp) will be a continuation of a construction camp for 300 people, which will be used for a full year prior to the start of production.