The first stage in any plant design is the definition of the project. This is referred to as writing the scope. Until the scope is established there can be no control of the project. Without a scope, it is impossible to determine what is germane and what, although interesting and related to the project, is actually extraneous information. Since the major goal of a preliminary process design is to provide a reasonably accurate cost estimate, the scope for such a project must determine what will and will not be included in this estimate. Working without a scope would be like trying to estimate the amount a woman entering a supermarket is going to spend when you don’t know if she is doing her weekly shopping or only buying snacks for a party.
The major cause of projects overrunning original estimates and getting cancelled after design engineering is nearly completed is an improperly conceived scope. Unless the engineer is very careful, the initial scope may not include everything that is necessary. Every time something is added, the estimated cost rises. If this projected cost increases too much, the project may be cancelled and the result will be a number of frustrated and disillusioned engineers and scientists.
As an example of an incomplete scope, consider the case of a person who decides to take up snow skiing. He has seen a television program on skiing in the Alps, and thinks he would enjoy it. He goes to his local sporting goods store and inquires about equipment. The salesman tells him that skis can be purchased for $30.00, the poles for $5.00 and a pair of boots for $45.00. After cogitating about it for a while, he decides that for $80.00 it’s worth a try. So he goes back to the sporting goods store and buys the skis, boots, and poles for the $80.00 quoted, plus tax. However, before he can ski there are a few added expenses he has not considered. He needs ski bindings to attach the boots to the skis. Good safety bindings cost $25.00 and their installation will cost $7.00. No ski area will allow him on the ski slopes without an Arlberg strap or its equivalent. This is a safety strap that prevents the loss of the ski if the safety binding releases. If a ski gets loose at the top of a hill, it can reach very high speeds on the ski run. Should this runaway ski hit a skier or spectator it could severely injure or kill him. The safety strap will cost $5.00 installed. Since he has spent $45.00 on boots it would seem silly not to buy a $3.50 boot-tree so that the boots will maintain their shape. Next, our friend finds out that the trunk of his car will not hold his 6 ft (2 m) skis. To get them to the ski slopes he will need to buy a $25.00 ski carrier that can be mounted on his car. At this point he has added $65.50
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to his initial estimated cost of $80.00. This is an 80% increase over his originally estimated price, and he had firm prices for the initial equipment. But this is not the end. He is going to find that there are more expenses. He will need a variety of waxes ($2.00) straps and a center block for storing the skis ($1.50), and specially designed leather ski gloves for use on rope tows ($8.00). Before long he will also purchase goggles ($4.00), ski pants ($30.00) and a ski parka ($25.00). The total cost is now $216.00 or 170% greater than his original estimate. It does not include tow fees ($4-$9 per day), ski lessons ($8-$13 per hour for a private lesson), transporta- tion to the ski slopes (a distance of maybe 100 to 200 miles each way), meals or lodging.
Although our skiing neophyte was interested in learning how much it would cost him to take up skiing as a hobby, this was not what was written in his initial scope. His initial scope was the purchase of skis, boots, and poles. With this scope he obviously would not be able to achieve his objective.
Another common example of an incomplete scope occurs when a person buys a car. The list price of a car may be around $3,000, but rarely does anyone pay under $3,500, and the price may reach $4,500. Most people do not want just a car. They also want certain extras: a radio, power steering, power brakes, bucket seats, a floor shift, whitewall tires, and so on. When a person asks the price of a car, he wants the dealer to include the extras. The dealer, on the other hand, gives the price of the stripped-down car, since he would probably scare the customer away if he included every possible extra in his quotation.
This same type of reasoning occurs in the chemical industry. When a project is evaluated the researcher would like to see the lowest possible cost attached to it, because then the probability of having it continued is enhanced. Other laboratories have competitive projects in the same way that there are many dealers competing to sell cars, so the projects that look most promising get the most money. On the other hand, management wants a reliable estimate of the total cost so it can decide whether a product can compete in the market place. It is up to the process engineer to see that the scope includes everything that is necessary to produce the required product safely, and nothing that is extraneous.
As an example of what should be included in the scope, suppose the manager of the product department sends you the following message: “We are considering building a plant to produce 60,000 tons per year of chlorine from the brine deposits near Pentwater, Mich. Would you please determine the cost of such a facility.” Does this define the scope? No! Definitely not.
In the production of chlorine from brine, caustic is produced. What is to be done with this caustic? Is it to be neutralized and discarded? If so, what acid is to be used and where is the resulting salt to be dumped? Will this cause pollution problems? Maybe there are no federal or state pollution laws being violated, but the fastest way to get restrictive controls is for the chemical companies to ignore the public’s feelings. On the other hand, if the caustic is to be purified and sold, how pure should it be, and can the amount produced be sold? When the brine also contains some magnesium salts and bromides, then the scope must indicate if magnesium and bromine are to be recovered, and, if so, what their respective purities should be.
Introduction to Chapter Three 59
There are different ways of producing chlorine from brine, for example, Dow cells, Hooker cells, and mercury cells. Which process is to be used must be known in order to make an accurate economic evaluation, since the capital costs and operating costs are different for each of these processes. The process engineer may have to investigate the different processes and economically evaluate each before deciding which process is best.
One of the major costs in the electrolytic production of chlorine is electrical power. Should the power be purchased, or is a power generating station to be built? If a power generator is to be built, should it be built large enough so that it can provide power for future expansions and for other existing plants the company may own in the general area? The answers to these questions will greatly affect the amount of capital the company must allocate for the project.
Since the product must be shipped to the customers, there must be transportation and loading facilities. It must be determined if docks, railroad sidings, pipelines, and/or roads need to be constructed, and what types of containers are to be used if all products are not to be shipped in bulk quantities.
While awaiting transportation and customer orders, the materials must be stored. How much storage should be provided for the products and raw materials? Whether a two-week or two-month inventory of products and feed are designed will affect the cost of the facilities, as well as the plant land area.
Another factor that will have a great bearing on the land area required, the plant layout, and the design is whether provision should be made for future expansion. Should enough space be left to add 50 additional cells and to double the storage space? Should the facility be designed so that these additional units can be con- nected easily into the process system? Should the purification and finishing steps be overdesigned so that when the expansion occurs only new cells need to be added? All these questions must be answered before any attempt can be made to obtain a valid cost estimate.
Let us return to the request of the product department manager to determine the cost of a plant for producing 60,000 tons per year of chlorine from the brine deposits near Pentwater, Mich. Does the process engineer give up because the scope is undefined? If he does, then he can be certain that his hopes for advancement are going to be greatly diminished. Industry is looking for the man who can take a difficult assignment and complete it with a minimum amount of time, money, and effort. Managers are rarely pleased by a man who offers excuses as to why things cannot be done. For the above problem they want an engineer who will recognize that the scope is incomplete, and who will scout out the information needed to complete the scope and the assignment.
By using his engineering experience and common sense, the process engineer can answer many of the above questions himself. The other answers can usually be obtained from one of his co-workers. In every company there are people of varied backgrounds. Usually someone can either provide an answer or suggest a place where the answer may be found.
The scope is a series of assumptions that everyone concerned with the process is expected to question. If one succinctly presents these and makes them generally
available, the hope is that any errors will be noted and corrected. For instance, sometimes when “percent” is said the listener may assume it refers to weight percent, whereas the speaker means mole percent. Another example is a formula- tion that calls for 5 lb of catalyst per 1,000 lb of feed. The engineer may infer this means 5 lb of solution containing 1 lb of active ingredient, where the scientist meant 25 lb of solution or 5 lb of active substance. Anyone who has dealt with people realizes that these communication errors occur all the time.
This is why it is important that the writing of the scope be the first thing done on any project. Then any errors can be corrected before the project has proceeded very far. Even if something is not known, the scope contains the best estimate of it. If this estimate is later found to be wrong, it is then corrected. Thus, the scope becomes a fluid document.
After the scope is approved by all concerned parties, any change is formally made on a paper entitled “Change of Scope.” These are distributed to all concerned parties, and are discussed at periodic meetings called to review the status of the project. The information that is necessary to define the scope is given in Table 3-l. The importance of these items will be discussed on the following pages.
THE PRODUCT
It is presumed that the product(s) to be produced is (are) known. The size of the containers it will be shipped in depends on the size of the expected orders, the facilities the customer has for handling the materials, and the hazardous classifica- tion of the material. Material shipped in bulk quantity is cheaper than packaged items, but it requires the customer to have more elaborate unloading and storage facilities. Bulk shipping is only used when large amounts are purchased at one time. Union Carbide will not ship in bulk less than 40,000 lb (18,000 kg) of material.’ Table 3-2 gives a summary of the maximum bulk shipments possible by various carriers.
Most large standardized containers made of rigid metal are 8 x 8 ft (2.4 x 2.4 m), and are 10,20,30, or 40 ft (3,6,9, or 12 m) long.* These can be transported by truck, boat, or train. Another type of container is a collapsible rubber bag known as a sealdbin. This has the advantage that when it is empty it does not take up much space, hence the cost of returning it to the sender is reduced. It has a7 ft, 2 in (2.2 m) diameter, and is 8 ft (2.4 m) high. Table 3-3 gives the standard sizes for some small chemical containers. A comparison of costs for shipping by different methods, plus the costs of small containers, is given in reference 3.
CAPACITY
The capacity of a plant depends, among other things, on how much material can be sold. This is predicted by marketing experts, on the basis of a marketing survey that indicates how much of each product can be sold by the company. This survey must predict what is likely to occur during the next IO-15 years. It must cansider end uses, competitors’ plans, competing products, market potential, and so on. The
The Product
Table 3-l
Items to Be Included in the Scope
6 1 1. 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10. 11. 12. 13. 14. 15. 16. 17. 18.
The product(s) (including package size) Quantity of each product
Quality of each product
Storage requirements for each product Raw materials for each product Quality of the raw materials
Storage requirements for the raw materials By-products
P r o c e s s t o b e u s e d , i n c l u d i n g y i e l d s a n d c o n v e r s i o n s Waste disposal requirements
Utilities requirements
What provision should be made for future expansions Location of the plant
Operating hours per year Completion date Shipping requirements Laboratory requirements Special safety considerations
Table 3-2
Maximum Bulk Shipments by Various Carriers
Petroleum tankers: 4,000,OOO bbl of oil*
Cargo ships for chemicals: Up to 290,000 bbl total Ocean barges: 26,000 tons
River barges: 3,000 tons of liquid 1 , 5 0 0 t o n s o f d r y s o l i d s Railway cars:
Hopper cars 125 tons (5,800 T a n k c a r s 1 0 0 t o n s ( 6 0 , 0 0 0 g a l ) Trucks:** 1,570 of dry solids
8 , 7 0 0 g a l l o n s o f l i q u i d
* Ships containing over 1 million barrels are too large to enter any U.S. ports. ** Weight limits set by states. See reference 2.
capacity also depends on technical and economic questions that the process en- gineer must answer.
The final decision on how large the plant will be is made by the board of directors. This, then, is one of the four major decisions made by them. The others are whether, where, and when to build. The factors the engineer must weigh in determining an optimum plant size will be considered next.
Table 3-3
Standard Size Small Containers for Chemicals