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Allen 8. King plant-Land acquisition to make up present proposed site
The Northern States Power Co.'s data sheet on page 2 shows the surface area of Lake St. Croix at normal pool as follows:
Acres From Stillwater Bridge to A. S. King plant site..
790 From A. S. King site to Chicago Northwestern bridge at Hudson.-
1, 320 From C. & N.W. Bridge to Prescott---
5,500 If we assume that the average depth of the river is 20 feet, then the total volume of the lake would be approximately 152,200 acre-feet.
The distance from Stillwater to Prescott, which is the length of Lake St. Croix is approximately 24 miles. The width of the lake varies from 2,000 feet to approximately a mile and has an average width of approximately 3,000 feet.
For the purposes of relating volume of Lake St. Croix to the circulating water requirements of the Allen S. King plant, we believe that only that portion of the lake above the Chicago Northwestern Railroad bridge at Hudson is of significance. The volume of water in this portion of Lake St. Croix is 42,200 acre-feet.
The Division of Waters of the Department of Conservation, State of Minnesota, Bulletin No. 11, published in August 1961 and entitled “Water Resources of Minneapolis-St. Paul Metropolitan Area,” show in figure 9 the duration curve of daily recorded flows in the St. Croix River at St. Croix Falls for the period of 1911-54. These duration curves show that the daily flow equaled or exceeded 95 percent of the time is about 1,200 cubic feet per second. The daily flow exceeded 90 percent of the time is about 1,500 cubic feet per second. The flow in the St. Croix River where it enters Lake St. Croix is equal to the flow in the St. Croix River at St. Croix Falls plus the contribution made by the Apple River. Northern States Power Co. annual duration curves of monthly mean flows at the plant site show that flows equaled or exceeded 99 percent of the time is 1,180 cubic feet per second, 95 percent of the time is 1,550 cubic feet per second, and 90 percent of the time is 1,750 cubic feet per second, with a minimum mean monthly flow of record of 913 cubic feet per second, which occurred in August 1934. The State's flows at St. Croix Falls corrolate very well with our curves which show the addition of the contribution of the Apple River.
In addition to the flow entering Lake St. Croix from the St. Croix River is a contribution made by the flow out of the Jordan sandstone which underlies the lake. We have no measurement of this, however, our temperature measurements indicate cool water at the bottom of the lake during the hottest part of the summer which may indicate some considerable volume of inflow contributed from the aquifer.
COOLING TOWER COST
There are three methods of using cooling towers at the Allen S. King plant unit No. 1 and two types of towers that may be employed. The two are the mechanical and natural draft towers. The mechanical draft towers have large fans which draw the air in through the tower sides, up through the water spray and discharges it out the top of the tower. These generally are long, rectangular structures with several fans on the top and with reinforced concrete basins below the tower in which to collect the water which is sprayed through the tower. The second type of tower is a natural draft tower which, as the name implies, has a natural draft and does not depend upon fans. This is a large diameter, conical shaped, structure up to 250 feet in diameter and 300 feet high.
The three schemes for employing cooling towers at the Allen S. King plant are as follows: Scheme A is to use the towers during periods when the lake water
is warm to reduce the temperature of the circulating water discharge from 5° to 10°. This is partial cooling. Scheme B employs a closed system for use during the summer only. As in scheme A the balance of the year the discharge would be to the lake. Scheme C is a closed year-around system where makeup water is added to the system to replace that which is lost through evaporation and water is cooled by use of the towers and recycled through the plant. Here the use of cooling towers in the winter is anticipated and it is evident that the mechanical draft tower would not be tolerable in this community because of the large amount of fog which would be discharged at a low level. Natural draft towers will release fog at a higher elevation and, therefore, would be less objectionable.
The following tabulation indicates the capital investment required in the various types of towers under the three schemes. Scheme A. Helper tower: Mechanical draft-
$1, 265, 000 Natural draft---
2, 875, 000 Scheme B. Closed system summer only: Mechanical draft
2,000,000 Natural draft---
3, 611, 000 Scheme C. Closed system year-around: Natural draft--
3, 795,000 It is obvious that the large capital investment for natural draft towers make them unattractive for use under schemes A and B. Therefore, we believe that it towers were to be installed at this site the choice would be mechanical draft towers. We have no choice under scheme C due to the fog problem. The operating cost of natural draft towers is very low. The operating and maintenance cost for mechanical towers is in the neighborhood of $50,000 annually. The carrying charges on the investment in mechanical towers under scheme A is approximately $190,000. The total additional cost of helper towers under scheme A is approximately $240,000 annually. The carrying charges on the capital invested under scheme B, closed cycle summer only, is $300,000 plus $50,000 operating cost makes a total annual cost of $350,000. The annual cost of the closed cycle year-around natural draft under scheme C is $570,000 plus approximately $10,000 in operating and maintenance making a total of $580,000 annually.
NSP_Total system (including NSP Wisconsin)-Generating capacity, by type of
fuel burned (as of Dec. 1, 1964)
NSP-Total system (including N8P Wisconsin)-Generating capacity, by type of
fuel burned (as of Dec. 1, 1964)–Continued
1,840 2,000 3, 400 1,840
500 4,000 4,000 4,000 1,100
175 1, 840 3,000
20 1, 840 1, 760 1, 840 1,840 2, 760
760 1,000 1,520 41, 035
1, 770 1,700 1, 770 1, 770 2,660
970 1, 470
Total, 21 plants.
540 1, 900 6,000
1,200 6,500 9,500
400 4,800 12, 400 33, 750
640 14, 400
160 5, 400
500 1,200 1,000
300 23, 200 1,200
600 35, 280 197, 180
1, 890 6, 150
195 16, 250 1,060 1, 400 8, 470
335 5, 970
1,970 33, 750
400 10, 600
200 1, 240
0 16C 5, 370
190 1, 350
2 3 1 10 2 1 2 1 2
50 21, 950 1, 180
350 31, 900
Total, 32 plants.---
1 None of these plants has a firm capability based on use of natural gas because natural gas is available to company for electric generation on an interruptible basis only.
Kilowatt-hour output data, 1963—Northern States Power Co., Minneapolis and suburbs
699, 095, 191 Diesel plants
2, 652, 555 Steamplants?.
8, 027, 473, 095
Percent * Steamplant fuel consumed (Mega B.t.u.) : Coal
58.7 oil (boller torches) Gas (natural and Koppers).
output * Steamplant kilowatt-hour output by fuels : Coal (including torch oil)
4, 728, 181, 653 Gas.
3, 299, 291, 442 Total.----
8, 027, 473, 095 NOTE.-All natural gas used for electric generation is available to company on an interruptible basis only, and therefore must have coal as a standby. Natural gas is generally not available during the period Nov. 16 to Mar. 16.
SO, REMOVAL FROM FLUE GAS From a practical point of view there appears to be no economical means of removing SO2 from flue gas. Considerable developmental work has been done in this direction and removal is accomplished on a comparatively small scale in England. One of the more well-publicized efforts is the project presently being undertaken by the Pennsylvania Electric Co. at their Seward station.
The results of this catalytic pilot plan operation at Seward Station indicates that full-scale commercial sulfur removal from the gaseous discharge of a steam generating plant is feasible, however, it has not been developed to a point where this process is practical for a plant the size of the proposed Allen S. King plant.
There are other methods of extracting SO2, some of which are outlined in the attached "review of literature." Our engineers have investigated the utilization of the Pennsylvania Electric Co.'s removal method and estimate that the total cost of installing the facility would be between $17 and $20 million. The calculated return from the sale of sulfuric acid recovered from the plant would be in the neighborhood of $1,560,000 per year. This indicates that the removal of sulfur by this method would be extremely uneconomical.
The report, in letter form, from our consulting engineers, Pioneer Service & Engineering Co., is attached which provides additional detail to supplement this statement.
SULFUR DIOXIDE REMOVAL FROM FLUE Gases REVIEW OF LITERATURE A number of methods are available to extract the sulfur dioxide from flue gaș (8). The more important ones are as follows (bibliography attached).
A. PROCESSES REGENERATIVE BY PHYSICAL MEANS
This process employs the reaction of dimethylaniline with sulfur dioxide and through an elaborate system regenerates the dimethylaniline and removes the sulfur dioxide in the form of dry gas. This process operates at high levels (5.5 percent) of sulfur dioxide with removal of 99 percent of the gas.
This process uses similar methods to remove sulfur dioxide. It is adaptable to concentrations from 1 to 16 percent SO2. At 7 percent SO2, the steam requirements are 1 to 1.2 per ton of SO, produced.
This process strips the so, from the fue gas with ammoniated salts and the final product is ammonia sulfate and sulfur. The process requires large amounts of ammonia. It can be operated at relatively low concentrations of 8oz.
Basic aluminum sulfate process
This process uses basic aluminum sulfate to strip the flue gas of So, and is regenerated with steam. The end product is sulfuric acid. This may be useful in concentrations down to 1 percent SO2.
B. PROCESSES REGENERATIVE BY CHEMICAL MEANS
Sodium sulfite-zinc sulfite process
The SO2 is removed with sodium sulfite and reacted with zinc. This process requires elaborate equipment, but gives almost complete removal of $0. Wet thiogen process
This process uses large quantities of water and is useful only at high SO concentrations.
C. NON REGENERATIVE PROCESSES
This process is very similar to the ammonia process, regenerative. Nearly
Lime is used to react with the So, to form an end product of calcium sulfate
Here the SO2 is absorbed by the alkalinity of the natural water and discharged into the river. Catalytic oridation to sulfuric acid
SO, is catalytically reacted with 0, in the flue gas and is converted to SO, which is extracted as H.S0s. This process has the advantage of working at low concentrations of so, and also operating at high temperatures. This is presently being used at Pennsylvania Electric Co.'s Seward Generating Station (3, 4, 6, 7). Alkalized alumina proce88 (5)
The SO2 is absorbed on alkalized alumina at high temperatures and regenerated from the alumina by a separate operation.
The physical regenerative processes are only adaptable to conditions where the SO, in the flue gases exceeds 1 percent. The chemical regenerative processes are not economically feasible, but operate best in 0.5 to 1 percent S02. Almost complete removal of so: can be achieved by these methods. The nonregenera. tive processes operate best at less than 1 percent and do accomplish almost complete removal of SO.. Product disposal becomes a problem here.
(1) Bureau of Mines Information Circular (7836, 1958, 96 pages) : "Sulfur Dioxide-Its Chemistry and Removal From Industrial Waste Gases."
(2) Institution of Chemical Engineers (Trans. V38, No. 2, 1960, pp. 54-62): “Development of Fulham-Simon-Curves. Flue Gas Washing Process," C. W. Wood.
(3) Journal on Applied Chemistry (vol. 8, 1958, pp. 781-786): "Catalytic Oxidation of Sulfur Dioxide at Low Concentrations,"
(4) Iron and Steel Engineering (41:167 May 1964): "System Eliminates Solids and Sulfur Fumes from Stack Discharge.”
(5) American Society of Mechanical Engineers Transcript (ser. No. A86:353-8 discussion 358-60 July 1964).: "Removal of Sulfur Dioxide From Flue Gas With Alkalized Alumina at Elevated Temperatures," D. Bienstock and others.