CHAPTER VIPOWER PLANT REQUIREMENT.
Steam Making Equipment — Uses of Pumps — Types of Pumps — Pumps for Brine — Water Supply — Pumps for Wells — Water Distribution Systems — Pumps for Boiler Feeding — Heating Boiler Feed Water — Wells — Cooling Towers — Economizers — Superheaters — Steam Engines — Exhaust Steam — Advice as to Exhaust Steam — Boilers — Conclusion.
Steam Making Equipment — Uses of Pumps — Types of Pumps — Pumps for Brine — Water Supply — Pumps for Wells — Water Distribution Systems — Pumps for Boiler Feeding — Heating Boiler Feed Water — Wells — Cooling Towers — Economizers — Superheaters — Steam Engines — Exhaust Steam — Advice as to Exhaust Steam — Boilers — Conclusion.
—The quantity and type of boilers needed for a plant is entirely dependent upon the quantity of steam required and its economical or uneconomical use. The refrigerating and electric producing apparatus in the average packing house are usually looked upon as the chief using elements, but they each frequently require less steam than is used for pumping purposes, and less than is used for cooking and kindred operations. It would be well to discuss the uses of steam and return to the boilers.
—Pumps are used for water circulating, brine circulating, boiler feeding and pumping products. These are named in the order of their steam consuming demand as it usually occurs. They consume from 40 to 120 pounds of steam per horse power hour based on the kind of pump used and the skill in its operation. The most economical are electrically operated centrifugal pumps provided the current is economically generated, steam turbine centrifugal pumps, next if in good condition, and reciprocating simplex or duplex pumps third and fourth.
—The types chiefly used in packing house work are simplex and duplex reciprocating, centrifugal single and multi-stage operated by motor or steam turbine directly attached to the motive power, also power pumps oftriplex type and rotary or impeller pumps for fats and oils. There are endless varieties of each type.
—For brine pumping chiefly reciprocating and direct connected horizontally set motor driven centrifugal pumps of one or more stages are used. At times power operated triplex pumps are used but the most satisfactory are the second named.
Pumping brine for refrigerating purposes is a never ending process since it must be constantly performed. The common practice of an open brine tank with submerged coils is being fast superseded by the use of shell and tube type closed coolers which superseded double pipe coolers. The use of either the latter two types enables the operator to take advantage of hydraulic head by installing a balanced system described in this work which very greatly reduces the power necessary to exert to pump brine. The friction in an eight to twelve pass brine cooler is from ten to fifteen pounds, and this with the pipe friction on a balanced system will total to perhaps thirty pounds on large systems, but less than the ordinary open system—depending upon the building height.
—The water demand for packing house operation is quite an important element in relation to steam consumption. The quantity required for ammonia condensing, steam condensing (if done), and for plant purposes, washing, etc., is, in the aggregate, quite a large amount. For example: For ammonia condensing, from 1¹⁄₄ to 1¹⁄₂ gallons per minute is required per ton of refrigeration developed; for steam condensing for steam engine from 32 to 40 pounds per pound of steam condensed; for boiler operation about four gallons per horse power per hour; for plant purposes from 250 to 3,000 gallons or more per hour, depending upon the size of plant and its intelligent use. It will be readily seen that those quantities will mount in power consumption if the head or pressure pumped against is high.
—Water pumped from wells is usually pumped by one of four methods:
For small plants where one or two wells will supply the water, the first named pump is usually used owing to cheapness of cost for installing and particularly if the water rises in the well to a height reachable by a suction type pump, viz: 23 to 25 feet. Power operated suction pumps are also available for this service. If the water be too low for the above named type to handle, deep well pumps with steam head serve pretty well and usually cost less than air pumped wells.
For larger plants, larger wells are installed and submerged centrifugal pumps or compressed air is used, the latter always as a last resort from a cost of pumping standpoint, although its simplicity and reliability appeals to many.
Submerged centrifugal pumps can be operated with steam turbine or motor set on top of shaft above ground. The motor operated set is the more economical, particularly if the current be generated at low cost.
—The intelligent laying out of water systems and the pressure pumped against is a factor worth great attention. It is far better to have pumps of proper proportions for the service intended, even though it involves the use of a separated piping system.
Taking advantage of water once raised to a high level in its return to service is a power saving. For example: It is usual to locate ammonia condensers at a point where there is a good circulation of air. This is done to permit the winds to carry away the moist air from about the condensers, together with the heat delivered up through it and to the air by the discharged gas from the ammonia compressors. From the catch pan beneath the ammonia condenser the water can be diverted through the steam condenser and if the shell be bought sufficiently strong in the case of a closed condenser, the water can be delivered to the suction side of a pump which in turn will deliver it for house use for cleansing purposes. If a barometric condenser is used, the water is delivered to a hot well from whence it can be pumped or flow to sewer.
—Dependent upon the size of plant and the pressure carried pumps are usually provided as follows:
—Every plant, large or small, should be equipped with boiler water heating devices. These are so common and the practice so usual that it is scarcely necessary to mention it but the writer has seen plants where the exhaust steam from pumps and engines was being thrown to the air and feed water pumped into boilers at low temperatures. There are two types: closed and open. In the first named the water is circulated through tubes enclosed in a vessel, the tubes surrounded by steam. In the open type the steam is brought in direct contact with the water and performs the heating in this manner. The closed types are used on the principle that no oil carried in the steam is passed to the boilers, but the latter type are usually equipped with an oil separator that eliminates the oil and prevents danger from this source.
—In most instances wells of various depths from 80 to 2,000 feet will find water. A few localities, however, do not yield water via wells and this is a poor situation from a packing house standpoint. The water from surface or shallow wells is, at times, improper for use on meats owing to contamination, in which case, resort must be made to other sources. In some localities the neighboring streams yield suitable waters but in this case sewage contamination must be guarded against. The quality of boiler supply water is an important factor in the boiler operation in its bearing to shutdowns for cleaning, blowing down, repairs, etc., all of which contribute to or impair economy.
—Where it is necessary to husband water for condensing ammonia or steam the use of cooling towers comes into play. These function by the cooling of water by evaporation, the evaporation abstracting the heat. There are various kinds—sprays over ponds, water dripping over spatter boards made in various ways, such as brush piled loosely; a checker work of wood slats; screen wire, etc. These usually depend upon the circulation of air in a natural way.There are various patented types, depending upon fans, to pass air through falling water. The efficiency is dependent upon the fineness of the water and the quantity of air passing through it, the relative humidity of the air controlling greatly the cooling effect.
—Where the utmost economy of fuel is striven for and on larger plants, these are installed. An economizer is a bank of cast iron flues placed in a position between the boilers and the smoke stack. Water is circulated through the tubes and the furnace gases pass about them. They are usually calculated upon to decrease the stack temperatures from 100 to 150 degrees—dependent upon its initial temperature and to heat the feed water one hundred degrees. This is a saving from a wasted source, since it is impossible to take up this heat in any boiler yet designed.
—In an earlier chapter reference was made to superheated steam. The office of this apparatus is to heat the steam to a higher point than it rises to, under ordinary boiler conditions. For instance, steam as delivered from the nozzle of a boiler is spoken of as “saturated” steam, but, if before use this is subjected to a further heating before it is used, it is said to be “superheated.”
Superheaters are of two types. They can be described as follows: A bank of coils located in the flame pass in the boilers, the steam within the coils and the flame on the outside; or a bank of coils in a separate furnace, the flame or heat generated in the furnace passing over the coils.
Steam superheated beyond 450° F. total sensible temperature requires especial pipe fittings, type of valves, and engines for reasonable safe operation, and renders an economy that a small plant cannot afford, due to the expenditure, to take advantage of.
—Owing to the cheapness of fuel in the United States, users have been satisfied with equipment at a low initial cost and in consequence pay bills continually by using uneconomical prime movers, viz.: ordinary steam engines of the simple Corliss type, using from 26 lbs. to 35 lbs. of steam per horsepower hour, or compound condensing at 15 lbs. to 18 lbs. of steam per horsepower hour or high speeddirect connected slide valve engine generator sets using from 35 to 50 lbs. steam per horsepower, depending upon load.
European engineers, where fuel costs are double and triple American fuel costs, have of necessity paid more attention to the subject of steam economy and have outstripped this country in design and use of economical steam engines, notably of the so-called “uniflow,” “drop valve,” “poppet valve,” or “Lentz” type and with the use of superheated steam, have reached much higher efficiencies. The fast increasing costs of fuel in this country have necessitated American builders resorting to high steam pressures with independent or integral superheaters in conjunction with steam boilers, and as a result American manufacturers are offering simple uniflow engines for high speed (say 200 r. p. m.) direct connection to electric generators. Also compound drop valve or poppet valve or Lentz types for slowly moving engines, viz.: 60 r. p. m. for connecting to ammonia compressors and in either case with steam at an initial pressure of 160 lbs. and ordinary superheat of 100° operating condensing, engines of the above types under the conditions named can be readily bought under guarantees to produce an indicated horsepower with the use of 12 lbs. of steam per horsepower hour.
The uniflow engine is now offered by several builders and is adaptable to most any service, atmospheric exhaust, condensing or against a back pressure using the exhaust for cooking or heating. There is but little advantage, however, in a uniflow engine under this circumstance unless it be the flexibility as to conditions of operation.
—The practice of using exhaust steam, that is steam which has passed through engines, for heating and cooking is considered economical. It is based upon the theory that the quantity of heat contained in a pound of steam that has been reduced in pressure from its initial or high pressure, say 100, to a low one—example 5 lbs., and then used for heating, etc., contains almost as many heat units as it did originally.
There are many places where this low pressure or exhaust steam can be used advantageously, but if extensively used, the likelihood will be to have long mains into which certainequipment will pass its exhaust and from which the demand will be spasmodic for cooking purposes and intermittent for heating, except during winter seasons, and as a result there is a considerable quantity of steam passed to the air at most times.
A careful analysis is necessary for intelligent use of this idea, since the maintaining of a balance owing to business fluctuations and changing seasons makes an almost unmatchable combination. During one season live steam will be used for make up, and at other times there is a surplus.
—Aside from heating feed water and drying where the requirement is constant, a better practice is probably to limit the extent of exhaust steam systems and use live steam for most purposes.
The sources of exhaust steam, engines or pumps, are operating usually twenty-four hours daily and constantly pouring steam into the exhaust mains, which is constantly radiating, leaking and the accumulated moisture is being trapped away to a sewer or feed water heater. The traps are usually just a little out of order, and the little leaks in multiple mount up fast.
Again the apparatus in almost any department used for cooking and manufacturing is irregular in its use and an actual record will show hardly to exceed six hours’ demand or use. Why operate engines and pumps at a disadvantage all the time for the sake of a supply six or eight hours daily? The engine and pump requirement increases rapidly with the exhaust steam pressure and requires larger production from the boiler.
Any power like that needed for pumping can be transmitted on a wire with far less loss than as steam through a pipe.
The recommendations then are: Produce electricity as cheaply as possible; if electricity is made, use high class equipment operating condensing and take advantage of superheat if possible; produce refrigeration or compress air with the same intelligence; perform all pumping with electrically operated pumps; distribute steam for all uses at high pressure, at high velocity through small pipes, well insulated and havethe heat at the process when needed; fit boilers so they can arise to a demand when needed with ample stack and draft; install stokers, if the plant will justify it; insulate the boiler walls and generate steam as cheaply as possible—and don’t waste it.
—The common types of boilers in the United States are the fire tube boiler and the water tube boiler. The first named kind is that which suggests itself to the reader when a boiler is mentioned and consists of a shell cylindrical in form with a head in each end into which tubes are expanded. In operation the water surrounds the tubes and the fire passes through them. The water tube boiler is the opposite of this. There are variations of these and boilers that are built using both principles in part. There are also Cornish, Lancashire and Yorkshire types used in England which are fire tubes using only one or two tubes. Where a plant requirement is up to 500 horsepower, the fire tube is the usual installation owing to its cheaper cost, and more units which enables more continuous operation, especially if a unit is out of service for cleaning, 100, 125 or 150 horse-power being the standard size units. If a plant requires 750 horse-power or more, installation of the water tube is preferable owing to their requiring less floor space, higher pressures are usually carried and they are regarded as more safe under these conditions. They can be forced to a higher output if demanded, which is an advantage in times of rush business.
—The mounting costs of fuel prompts the writer to say that the management of a power plant of any packing house demands intelligence in the selection of equipment and in its operation. The losses that occur are silently passing on perpetually and are immeasurable to the proprietor since they are intangible in dollars and cents. In these days of educated engineers, a mixture of education and common sense is obtainable and it takes this training or the practical man who has augmented his practice with ability to use a pencil to figure out his conditions, and suggest remedies that will stop a leak of no inconsiderable consequence. It is a usually neglected department by the proprietary interests.