Suppose that you were hired by a paper mill as an engineer, which is planning to
ID: 2078899 • Letter: S
Question
Suppose that you were hired by a paper mill as an engineer, which is planning to use some of its waste products as an energy source from excess process steam, it means that the management is looking for installing turbine generators to produce electricity. Assume that the company has the following choices Three 10MW turbine generators, or One 20MW and one 10MW turbine generator, or A single 30MW turbine generator. As a company's engineer, you were asked to give your opinion/recommendation about three given choices to build this new electric co-generation facility. Also, the company advised you to consider cost, reliability and efficiency as the most important factors while giving your recommendation What will be your choice/recommendation? Justify your answer by explaining the advantages and disadvantages of each choice and support your claiExplanation / Answer
The company should use either 1) Three 10MW turbine generator or 2) One 20MW generator and one 10Mw generator
ADVANTAGES :
A) Reliability
When it comes to the reliability of mobile generation, parallel generators are the way to go. If you have one large generator, and this generator malfunctions, you will have no other backup options on site to take over the electrical load. It could take hours, or even days to get a replacement generator. Trucking could become another cost factor considering that most generators of this size are skid mounted. When you use paralleled generators, you now have the ability for generator redundancy. Typically electrical loads are sized with room left over for some redundancy. When you have a generator fail, the controller in the other generators senses the increase of load, and proceeds to carry the excess load over to the remaining generators. This in turn allows the company to never lose power. When properly installed this generator can then be easily swapped out without shutting down all of the current operation of equipment, and losing valuable production time.
B) Flexibility
When using multiple generators rather than one large generator, the setup allows for more flexibility. If you had a micro-grid setup on a location, and you needed to expand, you would not be able to do this easily with one large generator. The company may have to acquire additional funds to get another large generator, when all that was needed is just a couple more Kw. With a parallel set up, you can add on additional generators one by one. The generators can be paralleled to create a multi Megawatt system. If the company needs to downsize, this also becomes an advantage when using a parallel set up. The company can just release one or more of the generators without having to lose hours of production time, or waiting on the rental company. Suppose the current capacity of the power plant is 500 MW, if after 2 year it plans to expand the capacity to 700 MW then it will be much costlier to replace the whole single generator setup and to buy a bigger unit. Rather it is economical to buy small individual alternator units which can be added in parallel to the bus bar system in order to reduce the initial capital investment.
C) Ease of Generator Maintenance
If a company chooses to rent one large generator over multiple generators with parallel capabilities, it becomes more of a hassle for both the generator rental company, and the customer. Typically a representative of the company would have to communicate with the rental company to plan a service. The representative would also need to be present in order to ensure that the equipment is functioning properly after the generator is serviced, and put back into operation. This wastes both company’s personnel time and valuable production time. With a parallel setup, there can be redundancy. The other generators can pick up the load if one generator needs to be shut down and maintain equipment operation. If there is just a two generator setup, you can still use a LTR E.M.P which will transfer the load to a relief generator that the technician will bring out when a service is needed. This eliminates the need for personnel, and shutting down daily operation for maintenance. This kind of connection is quite feasible when the repair and periodical maintenance work is concerned. It is easier for maintenance when smaller individual generating units are used, since we can schedule the maintenance of each unit one after the other without affecting the continuity of power generation. While if we are using a single unit then the whole system has to be shut down for its maintenance work, this would definitely affect the power demand during that duration.
D) Cost Effectiveness
The generators in LTR’s fleet that are parallel capable are natural gas generators, and can run off either well head or propane gases. The ability to run off of well head gas eliminates the need for diesel fuel. The customer can expect to see thousands of dollars in savings per month by using produced gas at their well sites. Not only is the cost of fuel minimized, you also create less risk of spills, or damage to roads due to heavy fuel trucks. If diesel fuel is a cost concern for your company, natural gas is the way to go. The natural gas generators have more features that you don’t get when renting diesel generator sets. The natural gas generators have an onboard GPS system that can run off of cellular service, and when cellular service is not available it switches to satellite communication. The customers can expect to have access to this technology and monitor the generators they have on rent from a computer, or any mobile device.
And so it can be seen, that parallel natural gas generators are the way to go. You have the reliability of knowing if any generator shuts down you will not lose valuable, and costly time. The flexibility allows for any kind of set up that a location may need. Ease of operation makes worries of maintenance no longer troublesome. And, your company will be saving money.
E) Efficiency:
You might have seen the efficiency versus load current curve of the generator, according to that the generator unit must run on full load, since efficiency is maximum when the load is 100%. So if we are using a single large unit then it is uneconomical to use it on lower loads. While if we use smaller individual units we can add up or switch off the generator units as per the load requirements in order to meet the maximum efficiency
F) Size of Alternators:
More the rating of the generator, huge is the size of the setup. It is very difficult to manage a single large alternator which may range around 1000 MVA or more. Rather if we are using small individual units connected in parallel, it will be easier to manage considering its size.
A system designer considers three principal issues when weighing the merits of a parallel system
Redundancy:Paralleling an incoming set with an out going set before the out going is switched out and shut down ensures a soft transfer of power and avoids loading the batteries of an UPS system.
Capacity:Paralleling for capacity allows additional sets to be powered up as load demand increases or switched out of a system as the load decreases.
UL codes: System designers can choose a variety of systems but must comply with UL891 and UL 1558 if paralleling with a utility.
Non-UL compliant controls may be used only on systems not connected to the utility
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