METHOD AND FACILITY FOR STATIONARY THERMAL HYDROLYSIS OF ORGANIC MATERIAL WITH TOTAL ENERGY RECOVERY

Abstract

Procedure for the thermal hydrolysis of organic matter in steady state, with a double steam explosion and total energy recovery, which consists, as a minimum, of the 1) feeding stage, stepped pressurization and sequential injection of low, medium and high pressure level steam; 2) first stage of hydrolysis by consecutive steam explosion operations with the production of medium pressure level steam and thermal reaction; 3) second stage of hydrolysis consisting of steam explosion and production of low pressure steam. An installation for the implementation of the process, which consists of comprising pumps for stepped pressurization, fluid-steam mixers, valves, mixers, decompression elements, tanks, piping and instrumentation and control systems.

Claims

1. Procedure for continuous thermal hydrolysis of any type of organic matter that, to fully recover the energy and optimize the hydrolysis kinetics, comprises at least of stages: 1) feeding, stepped pressurization and sequential injection of low, medium and high pressure levels steam; 2) first stage of hydrolysis by consecutive steam explosion operations with the production of medium pressure level steam and thermal reaction; 3) second stage of hydrolysis consisting of steam explosion and low pressure steam production.

2. Process according to claim 1 and different from currently existing processes, is characterized by a step of feeding, pressurization and sequential injection of heating steam, characterized by: use a stepped pressure increase system, which allows to receive and take advantage of different pressure levels steam. In any circumstance the steam coming from the tanks (3) and (4) are injected into the system. According to the laws of thermodynamics, this procedure allows a total recovery of energy, without the need to operate with high concentrations of organic matter. use systems with at least two pumps, which when stepped pressurized, allow the proper injection of steam in the corresponding liquid-gas mixers. due to the effect of staggering pressures, use centrifugal pumps instead of positive displacement pumps, which are more expensive and difficult to maintain. reach temperatures and pressures on the feed to the hydrolysis stage (11) of up to 220 C. and 22 barg, higher than conventional. use low pressure steam mixing systems that allow to lower the pressure on the chamber of the second flash (4) to values between 0 and 0.5 barg, with the consequent decrease in the outlet temperature of the hydrolyzed organic matter and its impact on net energy consumption. use ultra-rapid systems for mixing live steam, so that the mixture to be hydrolyzed is only at a temperature higher than the secondary reactions' appearance temperature for less than 5 seconds. In such short times the extent of secondary reactions is negligible.

3. Process according to claim 1 and in a different way to those currently existing consists of a first hydrolysis step, characterized by: use a sequence of steam explosion+thermal reaction stages, which improves the overall kinetics of the process by reducing the size of the facilities. use a tank (3) that simultaneously operates as a flash tank, facilitating a first breakdown on the physical structure of organic matter, and as a reactor that facilitates the hydrolysis reaction by temperature. apply the temperature hydrolysis reaction to sludge that has previously undergone a steam explosion process, with which the reaction kinetics is significantly increased, allowing operating at temperatures between 140 and 180 C. and reaction times of less than 15 minutes.

4. Process according to claim 1 and different to those currently existing, consists of a second hydrolysis step, characterized by: making a second steam explosion from pressures between 3 and 10 barg up to pressures between 0.5 and 0.5 barg. producing a low-pressure steam that is conducted to the stage 1 of claim 1.

5. A process that according to the preceding claims and in a different way to those currently existing operates not only continuously but also in steady state with the consequent stability of the process and ease of control, which gives the procedure a great operational robustness.

6. An installation (1) for continuous thermal hydrolysis of organic matter, which according to claims 1, 2, 3, 4 and 5 can treat any type of solids and is especially suitable for treating sludge produced in residual water treatment plants and that achieves energy self-sufficiency by operating with lower concentrations of dry matter than those required by existing technologies. The installation includes: at least two pumps (20) and (21) for the stepped pressurization of organic matter fed. In the first phase, the pressure of the stream (9) rises to values between 3 and 8 barg. In the second phase, the pressure of the stream (11) is raised to values between 10 and 22 barg. at least three static or dynamic fluid-steam mixers (17), (18), (19), which allow a stepped increase in temperature, taking advantage of at least the low (13) and medium (15) pressure steam produced in the flash stages. valve (14) that can act as a pressure or cut control valve. Mixer (17), which depending on the characteristics of the feed (5) can be an ejector, thereby reducing the tank pressure (4) to values between 0 and 0.5 barg. a mixer (19) that receives live steam and which, in order to prevent the occurrence of secondary reactions, operates with mixing times of less than 5 seconds. a stream (11) whose pressure values (up to 22 barg) and temperature (220 C.), far exceed the limits imposed by other technologies. decompression elements that can be selected between constrictions, nozzles or valves (22) and (23) that are dimensioned according to the flow rate to be treated, to produce the pressure drop generated by the steam explosion mechanism. In the device (22) the inlet pressures may vary between 10 and 22 barg, with a maximum outlet pressure of 8 barg. For the device (23) a maximum inlet pressure of 8 barg, the outlet pressure moves in a range between 0.5 to 0.5 barg. tanks (3) and (4) that operate as flash chambers in which medium pressure (15) and low pressure (13) steam are produced, which when condensed are used to increase the temperature of the organic matter to be hydrolyzed. Likewise, the tank (3) acts as a reactor. The operating temperatures in the tank (3) can be set between 140 and 180 C., while in the tank (4) they are set between 80 and 110 C. instrumentation and control systems, not indicated in FIG. 1, so that according to claim 5, which implies steady state, allow to pre-set and maintain constant the desired value of any of the operation variables at all points of the installation.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0019] FIG. 1 shows a diagram of the installation for the implementation according to the invention.

EXPLANATION OF AN EMBODIMENT

[0020] Following FIG. 1 the procedure is described according to the invention claimed and the means used to perform an installation.

[0021] The means used are: tanks or deposits (2), (3), (4); mechanical impulsion and fluid pressurization equipment (20), (21); fluid-steam mixers (17), (18), (19); expansion elements (22), (23).

[0022] In the selected variant, sewage sludge is hydrolyzed, previously concentrated and at room temperature (5). In the ejector (17), the feed mixture (5) is produced, with low pressure steam (13) and with the recirculation stream (7). The output stream (8) of the ejector is returned to the deposits (2), in order to close a recirculation loop. All low steam (13) condenses in the system. Depending on the design conditions and the recirculation flow rates imposed, the stream (9) exiting the recirculation loop has a temperature between 70 and 100 C. and a pressure with values between 3 and 8 barg.

[0023] The stream (9) after the first pressurization and heating stage receives the medium pressure vapor (15) in the mixer (18). According to the energy balances, in the operating conditions the temperature after the incorporation of medium and high-pressure steam streams moves between 120 and 160 C., without reaching the thermal level corresponding to the development of secondary reactions. This fluid (10) is pressurized by the pump (21), reaching pressures between 8 and 20 barg. In the ultra-fast mixer (19) the fluid receives a live steam injection (16) with a pressure between 10 and 22 barg, capable of raising its temperature to 160-220 C.

[0024] After this ultra-rapid heating, the high temperature and pressure sludge (11) passes through the decompression element (22) and splits in the tank (3) in a medium pressure steam stream (15) which is conducted to the stage 1 and in a liquid stream (12). The liquid is kept in the tank (3), during a predetermined time, which varies between 1 and 15 minutes. With this sequence the organic matter is first subjected to a steam explosion process and then to a reaction process by thermal process. Consequently, the tank (3) fulfils the double function of flash tank and reactor. In the case described, the temperature inside the tank (3) is maintained at a pre-set and controlled setpoint value between 140 and 180 C.

[0025] After remaining in the tank (3) during the pre-set reaction time, the pre-hydrolyzed organic material stream (12), with a pressure between 3 and 9 barg, passes through the decompression element (23) and into the tank (4), which acts as a flash chamber, splits in a low pressure steam stream (13) that is carried to stage 1 and in a stream (24) of hydrolyzed sludge that is brought to digestion. The tank pressure (4) can vary between 0.5 and 0.5 barg. In the variant described and with the ratio of liquid recirculating the pump (20) the pressure in the tank (4) is 0.1 barg and the outlet temperature of the stream (24) is 97 C.