Energy efficient system and process for hydrolyzing sludge

The present process relates to thermally hydrolyzing sludge in a thermal hydrolysis system. A flash tank or waste heat boiler is located downstream of the thermal hydrolysis system. Hydrolyzed sludge is continuously directed into the flash tank or waste heat boiler for recovering supplemental steam. The supplemental steam is used independently or in combination with live steam produced by a main boiler to heat sludge being directed into the thermal hydrolysis system.

FIELD OF THE INVENTION

The present invention relates to systems and processes for treating sludge or organic waste, and more particularly to a system and process for thermally hydrolyzing sludge or organic waste.

BACKGROUND OF THE INVENTION

Various systems and processes are employed to treat sludge and organic waste. For example, sludge and organic waste are sometimes subjected to a thermal hydrolysis process which may occur before or after anaerobic digestion. A thermal hydrolysis process causes cell walls to rupture under conditions of high temperature and high pressure and generally results in highly solubilized sludge which is more easily biodegradable. In particular, thermal hydrolysis employs high temperatures in the range of 130° C. to 180° C. and high pressure, typically in the range of 3-10 bar abs. When used in conjunction with anaerobic digestion, a thermal hydrolysis process decouples long chain polymers and hydrolyzes proteins and generally thermal hydrolysis transforms the sludge or organic waste in ways that makes anaerobic digestion more efficient.

Thermal hydrolysis processes consume huge amounts of energy. Temperature and pressure in the desired ranges for hydrolysis of sludge is typically created by injecting and mixing steam with the sludge in a hydrolysis reactor. Steam injection is a highly energy intensive aspect of sludge hydrolysis and waste energy recovery is a matter of significant concern relative to sludge hydrolysis. In some instances, it is known to partly recover energy by flashing off the steam into the incoming sludge in a batch hydrolysis process or by heating boiler feed water for the production of new steam. These processes are characterized by less than desirable efficiency and very high cost.

Therefore, there is and continues to be a need to improve the energy efficiency of thermal hydrolysis systems and processes.

SUMMARY OF THE INVENTION

The present invention relates to a thermal hydrolysis system and process for hydrolyzing sludge or organic waste that, on a continuous basis, recovers a substantial amount of the energy used in the thermal hydrolysis process.

In some embodiments, hydrolyzed sludge is directed to a waste heat boiler and used to heat boiler feedwater and form steam that is used to heat sludge being directed into the thermal hydrolysis system. In some cases, steam produced by the waste heat boiler is combined with steam produced by a main boiler.

In other embodiments, a flash tank is disposed downstream of the thermal hydrolysis system. Hydrolyzed sludge is continuously directed into the flash tank and by providing a controlled pressure drop between the thermal hydrolysis system and the flash tank, steam is continuously flashed in the flash tank. This steam is recovered and used independently or in combination with steam produced by the main boiler to heat sludge being directed into the thermal hydrolysis system.

In addition, disclosed herein are several options for efficiently mixing steam generated by the waste heat boiler, flash tank or main boiler with the sludge being directed into the thermal hydrolysis system.

In one embodiment, the present invention entails an energy efficient method for thermally hydrolyzing sludge. This method includes directing the sludge into one or more steam-sludge mixers. From the steam-sludge mixers, the sludge is directed to a thermal hydrolysis system where the sludge is thermally hydrolyzed and forms thermally hydrolyzed sludge. In the process, there is a main boiler. A first feed water is directed to the main boiler and the main boiler produces live steam. In addition, the method utilizes the heat associated with the thermally hydrolyzed sludge to produce supplemental steam. The method further comprises combining the live steam and the supplemental steam to form a steam mixture and mixing the steam mixture with the sludge in at least one of the steam-sludge mixers or alternatively, separately mixing the live steam and the supplemental steam in the one or more steam-sludge mixers. By separately mixing, it is meant that the live and supplemental steam is mixed with the sludge before the live and supplemental steam are mixed together. One example of this is where live steam is directed into one mixer and supplemental steam is directed into another mixer. The method described herein can produce the supplemental steam by one of two processes. First, this can be achieved by directing the thermally hydrolyzed sludge from the thermal hydrolysis system to and through a waste heat boiler and feeding a second feed water into and through the waste heat boiler to produce the supplemental steam. The second option is to direct the thermally hydrolyzed sludge from the thermal hydrolysis system to a flash tank and through a pressure drop between the thermal hydrolysis system and the flash tank producing the supplemental steam in the flash tank.

In another embodiment of the present invention, the method entails an energy efficient process for thermally hydrolyzing sludge by directing sludge into a steam-sludge mixer and thereafter directing the sludge to a downstream thermal hydrolysis system that produces thermally hydrolyzed sludge. The method entails feeding a first feed water to a main boiler and producing live steam. The method further includes utilizing heat associated with the thermally hydrolyzed sludge to generate supplemental steam. This is achieved by directing the thermally hydrolyzed sludge into and through a waste heat boiler and feeding a second feed water into and through the waste heat boiler and heating the second feed water to produce the supplemental steam. The method also includes directing the live steam from the main boiler through a steam line having a steam injector therein. The supplemental steam is injected into the steam line via a steam injector and mixed with the live steam to form a steam mixture in the steam line. The method entails directing the steam mixture into the steam-sludge mixer located upstream of the thermal hydrolysis system and mixing the steam mixture with the sludge therein.

In another embodiment of the present invention, the method for thermally hydrolyzing sludge includes directing the sludge into one or more steam-sludge mixers. Then the sludge is directed from at least one of the mixers to a thermal hydrolysis system which produces thermally hydrolyzed sludge. There is a main boiler that receives a feed water and produces live steam. This live steam is directed from the main boiler through a steam line to one or more of the steam-sludge mixers located upstream of the thermal hydrolysis system. The method further includes utilizing the heat associated with the thermal hydrolysis system to generate supplemental steam. This is achieved by directing the thermally hydrolyzed sludge into a flash tank and maintaining a pressure drop between the thermal hydrolysis system and the flash tank so as to cause the flash tank to produce the supplemental steam. Thereafter, the method entails directing the supplemental steam from the flash tank to at least one of the steam-sludge mixers located upstream of the thermal hydrolysis system.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

With further reference to the drawings, a system for treating sludge or organic waste is shown therein and indicated generally by the numeral100. The term “sludge” is used herein and encompasses organic waste. With particular reference toFIGS. 1-3, it is seen that the system100for treating sludge includes a hopper4for receiving and holding sludge and a conveyor32disposed in the bottom of the hopper for conveying sludge therefrom. Disposed on the outlet side of the conveyor32is a pump6which may comprise a progressive cavity pump. Pump6is operative to pump sludge to a sludge-steam dynamic mixing unit5. Typically the retention time of the sludge and steam in the mixing unit5is less than 5 minutes and the speed of the rotor in the mixing unit is greater than 2,000 revolutions per minute. In the embodiment illustrated inFIG. 2, there is provided a pair of sludge-steam mixing units5A and5B. In theFIG. 2embodiment, there is provided a pump6B operatively interconnected between the mixing units5A and5B.

Downstream of the sludge-steam mixing unit is a thermal hydrolysis system indicated generally by the numeral102. In the case of the embodiments illustrated herein, the thermal hydrolysis system102comprises three batch reactors or tanks1,2and3. A series of sludge inlet lines18,20and22are operatively interconnected between the reactors1,2, and3and the sludge-steam mixing unit5. In addition, there is a series of sludge outlet lines17,19and21that extend from the reactors1,2, and3and are employed for conveying sludge from the respective reactors. In addition, each thermal hydrolysis reactor1,2, or3includes a vapor outlet valve25for discharging non-condensable gases from the reactors.

Sludge outlet lines17,19and21lead to a waste heat boiler7. Waste heat boiler7can assume various designs and forms. In one exemplary design, the waste heat boiler7includes a series of tubes that extend through a substantial portion of the boiler. As seen inFIG. 1, the waste heat boiler7includes a sludge outlet that connects to line40that extends through or in operative relationship with two heat exchangers, heat exchangers12and13. Downstream of the heat exchanger13is a pump14for pumping the sludge in line40, in one example, to an anaerobic digester (not shown). In addition, waste heat boiler7includes a feedwater inlet42and a steam outlet line44. The thermal hydrolysis system100can be employed with or without an anaerobic digesting process. Furthermore, even when employed in conjunction with an anaerobic digester, the thermal hydrolysis system100can be employed upstream or downstream of the anaerobic digester.

The system and process disclosed herein employs various means to cool the sludge in sludge outlet line40. In one embodiment, a pump34is employed to direct treated wastewater through the cooling heat exchanger13for the purpose of cooling sludge passing therethrough. In addition, there are some cases where it may be desirable to dilute the sludge passing in line40. In this case, a class A dilution water can be pumped by pump33and injected at one or more locations along sludge outlet line40.

In addition to the waste heat boiler7, there is also provided a main boiler10for generating steam that is used to mix with the incoming sludge. Accordingly, boiler feedwater, potable water, is pumped to a water treatment unit15for treating the feedwater prior to the feedwater being introduced into either boiler. After treatment in the water treatment unit15, the boiler feedwater is directed through heat exchanger12and generally functions to provide additional cooling to the sludge passing through sludge outlet line40. Feedwater from the heat exchanger12is directed to a deaerator11. In the deaerator, non-condensable gases, such as CO2and O2, are stripped from the feedwater. Various types of deaerators can be used. In the embodiment illustrated herein, steam from the main boiler10is directed through steam line46to the deaerator11where steam contacts the feedwater flowing through the deaerator and removes certain gasses. From the deaerator11, the feedwater is pumped by pump31to main boiler10, waste heat boiler7or into a water injection line48. A series of valves, valves23A,23B and23C, control the flow of feedwater from pump31to the boilers7and10, as well as to the water injection line48. As seen inFIG. 1, pump31is operative to pump the boiler feedwater through valve23A and through line50to the main boiler10. In addition, pump31is operative to pump the feedwater through valve23B and through line52to a tank54which is also communicatively connected to the steam line44leading from the waste heat boiler7. Valve23C controls the flow of feedwater from pump31through the water injection line48. In practice, valve23C is controlled or opened and closed by an actuator.

A steam line58extends from the main boiler10for conveying steam produced by the main boiler. Disposed in steam line58is a steam injector8which is also communicatively connected to a lower pressure steam line60(FIGS. 1-3) extending from tank54. Various forms of steam injectors8can be employed. In one embodiment, the steam injector8takes the form of an eductor which is operative to induce steam produced by the waste heat boiler7from steam line60into the main steam line58where steam produced by the main boiler10and the waste heat boiler7are mixed.

Downstream of the steam injector8is a water injector9that is also disposed in the main steam line58. Water injector9is communicatively connected to the water injection line48. A valve24disposed in the water injection line48controls the flow of water to the water to injector9. In one embodiment, a temperature sensor is associated with steam line58for sensing the temperature of the steam passing therethrough. When there is a need to cool the steam in steam line58, the temperature sensor is operative to actuate the control valve24to reduce the temperature of the steam in line58.

As seen inFIG. 1, steam that flows downstream of the water injector9is directed to the sludge-steam mixing unit5where it is injected and mixed with the sludge prior to the sludge being directed to the thermal hydrolysis batch reactors1,2and3.

FIG. 3shows an alternate embodiment where steam line58leads to the conveyor32in hopper4. Sometimes this is referred to as injecting steam into the “live bottom” of the hopper4. In some embodiments, it is contemplated that the steam used to heat the sludge is injected into the “live bottom” of the hopper4. In such cases, there may not be a sludge-steam mixing unit downstream. In other embodiments, a portion of the steam is routed from steam line58into steam line62which is operative to deliver steam to the sludge-steam mixing unit5. In this embodiment, steam is directed at two points and the sludge is mixed with steam at the conveyor location, as well as in the sludge-steam mixing unit(s). See, for example,FIG. 3.

Turning now to embodiments shown inFIGS. 4-9, auxiliary or supplemental steam is produced by a flash tank35located downstream from the thermal hydrolysis system102. In particular, hydrolyzed sludge from the batch reactors1,2, and3are directed into the flash tank35. As discussed later, there is a control pressure drop between the thermal hydrolysis system102and the flash tank35. Steam is flashed out of the flash tank35by a pressure reduction which occurs by controlling or opening valve37. As shown inFIGS. 4-9, the flashed steam in flash tank35represents recovered energy from the thermal hydrolysis process and is used to heat succeeding batches of sludge in the batch reactors1,2, and3.

In theFIG. 4embodiment, steam from the flash tank35is connected through steam line64to the conveyor32or “live bottom” of hopper4. Steam produced by the biogas boiler10is directed through line58to the downstream sludge-steam mixing unit5. Therefore, in this case, steam is mixed with the sludge at two locations upstream of the thermal hydrolysis system102. In theFIG. 5embodiment, steam collected in the flash tank35is directed through line64to parallel pulpers16that are located between pump6and the sludge-steam mixing unit5. Pre-heating tanks, like a pulper, will have a retention time of the sludge longer in comparison with the dynamic mixer. Mixing in pre-heating tanks or pulpers is usually provided by a recirculation pump. In this case, steam in the main live steam line58can be directed to the sludge-steam mixing unit5or to the parallel pulpers16or to both. Turning to the embodiment shown inFIG. 6, steam collected in the flash tank35is directed through line64to a first sludge-steam mixing unit5A while steam from the main boiler10is directed to the downstream sludge-steam mixing unit5B. Steam collected in the flash tank35of theFIG. 7embodiment is directed through steam line64to a recirculation loop that includes pump31. The recirculation loop is communicatively connected to the pulper16and recirculates sludge through the recirculation loop. Steam in the main live steam line58is directed to the downstream sludge-steam mixing unit5.

The process depicted inFIG. 8is similar in many respects to the process described above and shown inFIG. 2, with the exception that the waste heat boiler7is replaced by the flash tank35. In the case of theFIG. 8embodiment, steam discharged from the flash tank35is induced by a steam injector or eductor8from line66into the main steam line58where the flash steam mixes with the steam produced by the main boiler10. In this case, the mixed steam in line58is directed to the first sludge-steam mixing unit5A. A portion of the steam produced by the main boiler10can be diverted through line62to the second downstream sludge-steam mixing unit5B. The embodiment shown inFIG. 9is similar to that shown inFIG. 8and discussed above, except that the combined steam in steam line58is directed to the “live bottom” of the hopper4. A portion of the steam produced by the boiler10can be diverted through line62to the sludge-steam mixing unit5.

The embodiment shown inFIG. 10excludes both the waste heat boiler7and the flash tank35. In this case, steam produced by the main boiler10is directed through line58to the sludge-steam mixing unit5. In the embodiment illustrated inFIG. 11, the waste heat boiler7and flash tank35are not incorporated into the overall system and process. However, the hydrolyzed sludge is directed from the thermal hydrolysis system102to a heat exchanger68that is operative to transfer heat from the sludge outlet line40to a sludge inlet line that extends between pump6and the sludge-steam mixing unit5.

Systems and processes discussed above are designed to obtain the lowest possible energy consumption in the course of thermally hydrolyzing sludge. This is made possible by optimizing the thermal hydrolysis process and recovering as much energy as possible. This is achieved, in part at least, by the employment of the waste heat boiler7or flash tank35. In both cases, heat energy associated with the hydrolyzed sludge is used to generate auxiliary or supplemental steam that is combined with or used in conjunction with live steam produced by the main boiler10.

Sludge from municipal or industrial wastewater treatment plants typically have a dry solids content between approximately 10% and approximately 40%. As discussed above, the sludge is mixed with steam at a point or points upstream of the thermal hydrolysis system102. Typically the steam is at approximately 150° C. to approximately 200° C. When mixed with sludge, the average temperature of the sludge-steam mixture is typically 140° C.-180° C. As discussed above, the sludge-steam mixture can be implemented in several ways. These are illustrated inFIGS. 1-11. In some cases, the sludge and steam are mixed in identical steam-sludge mixers. In other cases, the steam is injected into the sludge and mixed therewith through an injection valve. In some embodiments, a pulper16or other convenient structure can be used to cause steam to be absorbed and mixed with the sludge. By adding the steam and heating the sludge, it follows that the viscosity of the sludge will decrease and hence the sludge will be more easily pumped or conveyed.

In the exemplary embodiments discussed herein, the sludge is fed to one of the at least three reactors or tanks1,2, and3depending on which tank is ready to receive the sludge. The sludge is retained in the tanks for approximately 10-20 minutes which, together with the high temperature of between 140° C.-180° C., insures the hydrolysis of the sludge. It follows that in the exemplary thermal hydrolysis process disclosed herein that each tank will operate in three modes: filling, retention and emptying. Reactors1,2, and3will preferably operate in parallel, which makes the overall process a continuous process. Each mode will occupy approximately 20 minutes. The pressure in each of the three reactors or tanks is defined by the temperature of the sludge, which at 165° C., will be approximately 7.0 bar absolute. One may also consider the pressure from the gases released by the heating of the sludge which is mainly carbon dioxide. Non-condensable gases will accumulate in the reactors over time. The top of each tank or reactor includes a device for venting the non-condensable gases generated during the course of the thermal hydrolysis process. Thus, the non-condensable gases will be vented during the operation of thermal hydrolysis system102.

After sludge has been retained for 20 minutes in a respective tank, the sludge is directed out an outlet line and to the waste heat boiler7. As noted before, the waste heat boiler7includes a series of tubes. In the case of one embodiment, the feedwater directed into the inlet42of the waste heat boiler7is directed into and through the tubes. The sludge, on the other hand, moves around the tubes and through the waste heat boiler7. Heat from the hydrolyzed sludge is transferred through the walls of the tubes to the feedwater and, in a typical example, this produces saturated steam in the range of 130° C.-150° C. Hydrolyzed sludge leaves the waste heat boiler via line40and passes through heat exchangers12and13. In a typical example, the hydrolyzed sludge flowing through the heat exchanger12will heat the boiler feedwater to approximately 95° C. before the boiler feedwater reaches the deaerator11. The hydrolyzed sludge flowing through heat exchanger13will further cool the sludge. In addition, cooling or dilution water can be added to the sludge in sludge outlet line40so as to achieve a dry solids content in the range of 8%-10% and a temperature between approximately 35° C.-55° C., which is an appropriate temperature range for both thermophilic or mesophilic digestion. There are various means for assuring that the sludge flows through the waste heat boiler7and the two heat exchangers12and13. It is contemplated that in some embodiments the pressure in the reactors1,2, and3is approximately 8 bar abs, which is sufficient to force the sludge through the waste heat boiler7and through the heat exchangers12and13. In any event, pump14, shown in the drawings, is a progressive cavity pump which will empty the tanks by a constant flow controlled by the level transmitter (load cells, for example)28,29or30of each tank. If the pressure in the system is sufficient, then the progressive cavity pump14can be exchanged with a valve or another device which will maintain an appropriate pressure. It is appreciated that when one reactor is emptied, then the pressure above the liquid in the tank decreases, and at a certain level in the tank, the water in the tank will start to evaporate slowly to insure a balance between the liquid in the tank and the gasses above the liquid surface at the actual temperature. The evaporation of the water will cool the liquid approximately 1° C.-2° C. Then the temperature of the liquid will be decreased from approximately 165° C. to 163° C. during the emptying of the tanks.

There is a risk that the sludge flashes or boils in the pipes from the three reactors to the waste heat boiler7. To avoid this risk of flash, it may be necessary to place the three reactors above the waste heat boiler7. In this case, the static pressure in the liquid will prevent flashing in the piping system so long as the pressure drop in the pipe system is not excessive or too high.

As discussed above, a main boiler10, which may be powered by biogas produced by an associated anaerobic digester, is used to generate a main steam stream. The feedwater to the boiler10is treated in water treatment unit15and pre-heated by heat exchanger12. Various types of pre-treatment systems can be employed to remove, for example, hardness and other scaling or fouling species. For example, the boiler feedwater can be treated with various types of membrane separation units or ion exchanges. After leaving the heat exchanger12, the feedwater is directed through the deaerator11where gasses are removed and from the deaerator at least a portion of the feedwater is pumped to the main boiler10via line50. SeeFIG. 1, for example. In addition to feeding the boiler10, the feedwater is directed into tank54and thereafter through line56into the feedwater inlet42of the waste heat boiler7. As discussed above, the heat energy associated with the hydrolyzed sludge passing through the waste heat boiler7causes steam to be produced from the feedwater. Both boilers7and10produce saturated steam. Waste heat boiler7, however, produces steam at a lower pressure than the main steam boiler10. For example, the waste heat boiler7typically produces steam at 140° C.-150° C. while the main boiler10will produce saturated steam at 200° C.-220° C. Steam produced by the waste heat boiler7is boosted by the steam produced by the main steam boiler10. That is, by employing the injector system or eductor8, steam produced by the waste heat boiler7is injected into steam line58where it mixes with the steam generated by the boiler10. If the temperature of the combined steam is above a threshold, then the combined steam can be cooled by injecting feedwater from line48into the main steam line58as shown inFIG. 1. As discussed above, the steam produced by the waste heat boiler7and main boiler10is routed to a point or points upstream of the thermal hydrolysis system102to form a sludge-steam mixture.

With respect to the embodiments employing the waste heat boiler7(embodiments shown inFIGS. 1-3), during startup, the steam supply is derived totally from the steam boiler10. This is the case until the waste heat boiler7comes into operation and is able to generate steam. Once the waste heat boiler7is in operation, it will continuously take on more of the load. Once in full operation or in a steady state of operation, the waste heat boiler will supply approximately 35%-40% of the steam required to be mixed with the incoming sludge and the remainder will be supplied by the main boiler10.

Turning to the embodiments shown inFIGS. 4-9, the processes shown therein are similar in many respects to the processes shown inFIGS. 1-3but wherein the waste heat boiler7is replaced by the flash tank35. In the embodiments ofFIGS. 4-9, hydrolyzed sludge is directed from the thermal hydrolysis system102and particularly from reactors1,2and3to the flash tank35. The pressure in the flash tank is maintained between approximately 1.4 and 2.7 bar, which corresponds to a temperature range of 110° C.-130° C. The pressure in the flash tank35is controlled by regulating the valve37to maintain a generally constant pressure in the flash tank35. There are various approaches to controlling the continuous flow of sludge from the three reactors1,2and3to the flash tank35. In one approach there is provided a continuous flow of sludge to the flash tank35controlled by a “static pressure loss” with feature38(a fixed orifice, for example) together with valves17,19and21. Here the main pressure drop is over the “static pressure loss” and the flow is controlled by the valves17,19, and21. Another way of controlling the flow of sludge from the reactors1,2and3to the flash tank35is an approach that does not employ the “static pressure loss”. This approach includes repeatedly opening and closing the valves17,19, and21. That is, one valve is open for a short period which will result in a relatively large flow to the flash tank35for a short period of time. Then the valve will be closed and there will, of course, be no flow to the flash tank35. This process of repeatedly opening and closing these valves is repeated over a selected period of time. The operation of these two approaches is controlled by the load sensors or level transmitters28,29, and30associated with the reactors1,2, and3.

Flash steam discharged from the flash tank35is used in a manner similar to how the steam produced by the waste heat boiler7is used. That is, flash steam discharged from the flash tank35is combined with steam produced by the main boiler10or, in some cases, used independently to heat incoming sludge to the thermal hydrolysis system102. For example, in the embodiment shown inFIG. 4, the steam produced by the flash tank is directed through line64to the “live bottom” of the hopper4where the steam is mixed with incoming sludge. Steam from the boiler10is directed through line58to the downstream sludge-steam mixing unit5. In the embodiments shown inFIG. 5, steam from the flash tank35is directed through line64to parallel pulpers16. Steam produced by the boiler10is directed through line58to either the sludge-steam mixing unit5or to the pulpers16or to both. In the case of the embodiment shown inFIG. 6, steam produced by the flash tank35is directed through line64to a first sludge-steam mixing unit5A while steam produced by the boiler10is directed to the downstream sludge-steam mixing unit5B. In theFIG. 7embodiment, steam from the flash tank is directed through line64to a recycle line associated with the pulper16. Again, sludge produced by the boiler10is directed through line58to the sludge-steam mixing unit5.

The embodiment shown inFIG. 8is similar in many respects to the embodiment shown inFIG. 2and discussed above except that the waste heat boiler7is replaced by the flash tank35. In any event, flash steam from the flash tank35is induced through line66by the steam injector8and caused to mix in line58with steam produced by the boiler10. The combined steam in line58is directed to a first sludge-steam mixing unit5A while a portion of the steam produced by the boiler10is diverted through line62to the second sludge-steam mixing unit5B. The embodiment shown inFIG. 9is similar in many respects to the embodiment ofFIG. 8except that the combined steam in line58is directed to the “live bottom” of the hopper4. In other words, the steam is injected into a portion of the conveyor housing and mixed with the sludge being conveyed by the conveyor32. The diverted portion of steam produced by the boiler10is directed to the sludge-steam mixing unit5.

There are many advantages to the systems and processes discussed above. First, the systems and processes provide an efficient use of energy. Both the waste heat boiler7and the flash tank35are incorporated and used to recover a substantial amount of energy that would otherwise be lost. Once recovered, the energy is continuously converted to steam and efficiently mixed with the incoming sludge. Secondly, the entire system is easy and economical to maintain. For example, by mixing steam with the sludge outside of the thermal hydrolysis reactors substantially reduces maintenance problems and costs.