Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-08-02
2001-12-04
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S613000, C210S742000, C210S175000, C165S299000
Reexamination Certificate
active
06325935
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sludge treating systems and more particularly to a predigestion pathogen reduction system.
BACKGROUND OF THE INVENTION
It is common practice to treat sludge for pathogens by heating the sludge and holding the heated sludge in one or more reactors for a certain time period. Typically incoming sludge is heated to approximately 70° C. and held in one or more reactors for approximately one hour. After being held in the reactor or reactors, the sludge is cooled and directed into a digester where the sludge is held for a selected time period. Further, in treating sludge for pathogens, it is known to heat the incoming sludge and cool the treated sludge by a network of heat exchangers. Essentially the heat exchangers remove heat from the treated sludge and add heat to the incoming sludge.
Cooling the treated sludge to a selected temperature is quite important. This is because the treated sludge is directed to a digester that is held at a certain temperature and if the treated sludge is of a temperature that substantially departs from the design temperature of the digester, then this can substantially and adversely affect the digestion process. Usually, in the case of a mesophillic digester, the sludge held therein is maintained at a temperature of approximately 35° C. To avoid adversely impacting the sludge held in the digester, it is common practice to attempt to cool the treated sludge leaving the reactors to a target temperature range of approximately 34°-38° C.
In most pathogen reduction systems, it is virtually impossible to precisely control the temperature of the treated sludge being directed to the digester. In some cases, the heat exchanger network utilized relies on sludge-to-sludge heat exchangers, that is, the treated sludge leaving the reactor or reactors is circulated through a heat exchanger through which the incoming sludge passes. Thus the degree of heat transfer that takes place is dependent in large part on the flow rates of the incoming sludge and the treated sludge. Suffice it to say that there is very little practical opportunity to precisely control the temperature of the treated sludge, especially in cold climates. As a result, many pathogen reduction systems produce a treated sludge that, although subject to passing through one or more heat exchangers, fails to meet the target temperature range prior to introduction into a digester. Indeed, the problem is significant because of the lack of control of the sludge and/or heat transfer medium passing through the heat exchangers and the fact that the systems are designed for constant flow rates for all seasons of the year. Thus while it may be easy to meet the targeted temperature range in summer months for a given system, it may be quite difficult to meet the targeted temperature range using that same system during winter months.
Furthermore, in sludge treatment systems the heat exchangers tend to accumulate a build up of material such as grease foulings and other deposits within their inner walls as a result of the continuous passing of sludge through the heat exchangers. Eventually the heat exchangers must be cleaned. Typically this requires that the sludge treatment process be halted in order that the individual heat exchangers can be cleaned. The cleaning process for heat exchangers is time consuming and laborious. Not only is it costly in terms of labor to clean heat exchangers, but the fact that the sludge treatment process has to be shut down results in an even greater cost.
SUMMARY OF THE INVENTION
The present invention entails a system and method for reducing pathogens in sludge prior to the sludge reaching a digester. The method entails directing incoming sludge through a first heat exchanger which heats the sludge prior to the sludge being directed into one or more reactors where the sludge is held at an elevated temperature for a selected time period. After the selected time period has elapsed, the treated sludge is then directed from the reactor or reactors to and through a second heat exchanger (which may include a number of sections) that effectively cools the sludge before the sludge is introduced into a digester. In one embodiment of the present invention, there is provided a closed loop conduit that channels a heat transfer medium through the first and second heat exchangers. The heat transfer medium effectively removes heat from the treated sludge and adds heat to the incoming sludge. In order to more precisely control the temperature of the treated sludge, a variable speed pump is associated with the closed loop heat transfer medium for pumping the heat transfer medium through the first and second heat exchangers. By controlling and varying the flow rate of the heat transfer medium, it is appreciated that the temperature of the treated sludge exiting the second heat exchanger and directed to the digester can be more precisely controlled to meet a target temperature range.
Further, additional temperature control can be realized by employing other heat exchangers within the pathogen reduction system. For example, the treated sludge may be directed through another cooling heat exchanger where the cooling medium is treated wastewater. In order to vary the heat transfer in this case, a variable speed pump can be utilized to pump the treated wastewater through the cooling heat exchanger so as to remove heat from the treated sludge. A programmable controller may be operatively connected to the variable speed pump for varying the flow rate of the treated wastewater through the heat exchanger so as to control the temperature of the treated sludge prior to it entering into the digester. In one embodiment of the present invention, a single programmable controller can be utilized to control a series of heat exchangers so as to optimize the amount of heat transferred to the incoming sludge while at the same time adjusting the temperature of the treated sludge such that it meets the temperature target range established for the treated sludge before it enters the digester.
Another aspect of the present invention entails a method and system for cleaning the heat exchangers. In this regard, a fluid such as treated wastewater is pasteurized and held within a supply tank. A pump is utilized to pump this pasteurized fluid to a point where it contacts a pipe cleaning device and then the pressurized fluid is used to drive or move the pipe cleaning device through one or more heat exchangers associated with the pathogen reduction system. As the pipe-cleaning device is driven through the heat exchanger, it along with the pressurized fluid cleans deposits such as grease foulings from the interior of the heat exchanger.
Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings, which are merely illustrative of such invention.
REFERENCES:
patent: 3296122 (1967-01-01), Karassik et al.
patent: 3655046 (1972-04-01), Trussell
patent: 3697417 (1972-10-01), Teletzke et al.
patent: 3876536 (1975-04-01), Pradt et al.
patent: 4276174 (1981-06-01), Breidev et al.
patent: 5067231 (1991-11-01), Mueller et al.
patent: 5618442 (1997-04-01), Christy
patent: 6047768 (2000-04-01), Buehler, III
patent: 6117203 (2000-09-01), Buchave et al.
Coats & Bennett P.L.L.C.
Kruger A/S
Upton Christopher
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