There are numerous situations and processes in which liquids that collect or are stored or used in basins accumulate or become contaminated with sediments. One common situation is in the case of cooling tower basins. A cooling tower is a structure over which circulated water that is to be reused as a coolant is trickled, or flowed for the purpose of reducing the temperature of the water by partial evaporation. A cooling tower basin is a sump or volumetric container for the circulated water which has flowed or trickled from the top of the cooling tower to the lowest part thereof. The walls of cooling tower basins are typically constructed of concrete and provide a basin depth typically varying from about three feet to about thirty feet. From the basin, the "cooled" water flows to the suction side of a pump, or a plurality of pumps, that forces the water under pressure through a variety of heat exchangers for which cooling is desired. The heated water from the heat exchangers is then conducted to the uppermost portion of the cooling tower and is deposited on the cooling tower in a spray or distributed in a manner so as to enhance temperature reduction by a partial evaporation. The function of cooling water is thermodynamic. Water from the cooling tower transits through heat exchangers, either interiorally or exteriorally of typical heat exchanger tubing, where it absorbs heat from substances having higher temperatures, which substances are typically gaseous or liquid. After this transit, the heated water is returned to the upper portion of the cooling tower and descends by gravity through the cooling tower structure, whereupon the water is cooled in readiness for another cooling cycle.
The efficiency of the cooling tower water function is inversely proportional to its temperature; i.e. the lower the temperature of the cooling water, the higher the efficiency of heat exchange with its exchange medium. In other words, the greater the temperature difference between the cooling water and its exchange medium, the more enhanced is the thermodynamic effect of the process. There are many natural and understood phenomena which degrade the efficiency of cooling water by increasing its temperature; and thereby decreasing the difference in temperature between it and its exchange medium. One of these efficiency degrading phenomena is corrosion and erosion of piping in the flow process which result in the deposition of ferrous or ferric materials in the water. These ferrous or ferric materials cause the water to retain heat and thereby preclude desired reduction in temperature as the water descends through a cooling tower system.
The chemical composition of the water as it emanates from its original source is also an efficiency degrading phenomenon, whether that source be from sub-surface aquafers; from rivers, stream, bayous, etc. For adequate efficiency, the water should be as free as possible from chemical compositions that degrade the heat exchange efficiency thereof during a cooling cycle.
In some cases, water treating chemicals are added into the cooling water stream to precipitate undesirable solids and to maintain the hydrogen ion number so that the solution is neither excessively acidic nor basic. Such treating water chemicals can interfere with the heat exchange efficiency of the water.
Virtually all cooling towers are located in open areas and are therefore susceptible to deposit of contaminants, such as wind-carried dust, silt, sand, etc., that enter the cooling tower basin and reduce the convective and conductive cooling of the water as it circulates through the heat exchanger or descends through the cooling tower. It is important to note that the depositions of these various sediments in the cooling tower basin accrue incrementally over a long period of time and result in a considerable decrease in the efficiency of the thermodynamic system. For this reason, it is necessary from time to time to remove these efficiency degrading contaminants from the cooling tower basin.
In the past, and currently, the general methods of cleaning sediment from cooling tower basins included cleaning of the cooling tower basin with the water removed from the basin and manual cleaning of the basin after the water has been removed. In one case, the cooling tower is taken out of service and "free" water is drained from the cooling tower basin. After this has been accomplished, laborers or divers enter the basin with shovels, scoops or other implements and manually remove the sediment to containers placed outside the basin wall. In another case, laborers or divers enter the basin with vacuum hoses and cause the sediment to be "sucked out" to liquid vacuum trucks which transport the sediment to a "dump site" for ultimate disposal.
The above methods or cleaning cooling tower basins are extremely costly to the system in that the cooling tower system and the heat exchanger equipment serviced thereby, i.e., the heat exchange complex, must be shut down during the period that basin cleaning operations are being conducted. The resulting discontinuance of the operation of petrochemical systems during this period can result in lost revenues amounting to tens of thousands of dollars per day and cessate during that period of time delivery of energy materials to the marketplace. Additionally, all of the chemically treated water drained from the basin must be transported to a site for safe ultimate disposal. A substantial volume of the water treating chemicals is lost and must be replaced, thereby resulting in considerable expense to the overall heat exchange process and thereby adversely affecting the competitive nature of the particular process involved.
Another method for accomplishing cleaning of cooling tower basins is typically conducted under conditions where the cooling tower remains in service and laborers or divers enter the basin with vacuum hoses and cause the sediment and a considerable amount of chemically treated water to be transferred to vacuum trucks. These trucks then deliver the effluent to a safe "dump site" for ultimate disposal. Here again, as mentioned above, a considerable amount of expensive water treating chemicals becomes lost in the cleaning process. It is desirable to provide a cooling tower cleaning process that enables the heat exchange system, the cooling tower and the process to continue under normal production and allows effective cleaning to promote efficient thermodynamic effect without the necessity for laborers or divers to enter the cooling tower basin and conduct cleaning operations.
According to conventional practice, when hauled to a dump site by a truck, effluent having a low viscosity is subject to a sudden shift of position as the truck abruptly turns, stops or starts, thereby causing difficult steering or even overturn of the truck; a problem the present invention has remedy for.
Another situation where sediments collect is in the oxidizing basins of sulfur conversion units, which are also known as tail gas conversion units. The units are used to remove sulfur from tail gas by a method sometimes called the "Stretford Holmes Process". The units use a liquid known as Stretford solution and the sulfur is carried by the Stretford solution through an oxidizing basin, which is a large convernous basin, to a froth pit. During operation of the unit, larger sulfur particles do not retain enough velocity to go through the unit to the froth pit. These large particles of sulfur settle to form a sediment in the oxidizing basin. As the sediment collects in the basin, the available volume of Stretford solution for use in the process is reduced, thereby making the process less efficient. Also, since the Stretford solution is very expensive, it is economically wasteful to have substantial volumes of the solution tied up as sediment.
Another situation that involves the accumulation of sediments is in oilfield reserve pits and waste ponds. Such pits and ponds contain all manner of chemical, industrial and petroleum wastes, which are environmentally detrimental. Methods have been suggested for treating the water in such pits and ponds, but mere water treatment does not eliminate or even deal with sediments.
It is therefore, a feature of the present invention to provide an improved method and apparatus for the separation of liquids from solids and for the safe disposal of the separated solids.
It is also a feature of the present invention to provide a novel method and apparatus for accomplishing cleaning of cooling tower and sulfur conversion unit basins while allowing tower and unit to remain in operation during the cleaning process.
It is also a feature of this invention to provide novel apparatus and method for removing sediment from cooling tower and sulfur conversion unit basins without necessitating entry of laborers into the cooling tower basin where such personnel might be subject to hazardous chemicals.
It is an even further feature of the present invention to provide a novel method and apparatus for accomplishing cleaning of basins where loss of liquid is maintained at a minimum during the cleaning process.
It is another feature of the present invention to provide a novel method and apparatus for cleaning cooling tower systems and sulfur conversion units whereby cleaning operations can be conducted on a frequent basis and the cooling tower water can be maintained at optimum thermodynamic efficiency.
Another feature of this invention is to provide a method to improve the safe hauling of effluent.
Other and further objects, advantages and features of the invention will become obvious to one skilled in the art upon an understanding of the illustrative embodiment about to be described and various advantages referred to herein will occur to one skilled in the art upon employment of the invention in practice.