AU2005313622B2

AU2005313622B2 - Process for increasing the capacity of an existing urea process

Info

Publication number: AU2005313622B2
Application number: AU2005313622A
Authority: AU
Inventors: Johannes Henricus Mennen
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 2004-12-09
Filing date: 2005-11-11
Publication date: 2011-08-25
Anticipated expiration: 2025-11-11
Also published as: CN101076512A; EA200701242A1; CN101076512B; EA011378B1; EG26100A; CA2586286C; AU2005313622A1; AR104203A2; WO2006061083A1; CA2586286A1; NL1027697C2; AR051992A1

Abstract

The invention relates to a process for increasing the capacity of an existing urea process comprising, in the high-pressure section of the process, a reactor in which carbon dioxide and ammonia react to form urea, a thermal stripper in which the process stream from the reactor is stripped by supplying heat or an ammonia stripper in which the process stream from the reactor is stripped by supplying heat with the aid of ammonia as stripping gas and a condenser in which the stripping gases are condensed, whereupon the condensate formed is returned to the reactor, in which process the N/C ratio in the reactor is between 2.8 and 3.3 mol/mol, the pressure in the high-pressure section of the process is between 13.5 and 16.0 Mpa, at least a portion of the process stream from the reactor is stripped in a CO stripper in which the process stream from the reactor is stripped by supplying heat and with the aid of carbon dioxide as stripping gas and the condensing capacity in the high-pressure section of the process is increased.

Description

WO 2006/061083 PCT/EP2005/012201 PROCESS FOR INCREASING THE CAPACITY OF AN EXISTING UREA PROCESS The invention relates to a process for increasing the capacity of an existing urea process comprising, in the high-pressure section of the process, a reactor 5 in which carbon dioxide and ammonia react to form urea, a thermal stripper in which the process stream from the reactor is stripped by supplying heat or an ammonia stripper in which the process stream from the reactor is stripped by supplying heat with the aid of ammonia as stripping gas and a condenser in which the stripping gases are condensed, whereupon the condensate formed is returned to the reactor. 10 Such an existing process is described in for example Ullmann's Encyclopedia of Industrial Chemistry, Vol. A27, 1996, p. 344-350 as the Snamprogetti Self-Stripping Process. In such a process ammonia and carbon dioxide are contacted in a reactor at a pressure of 15.0-16.5 MPa and at an N/C ratio of 3.0-4.0 mol/mol. The 15 process stream that forms in the reactor is passed to a high-pressure stripper in which this process stream is heated in order to decompose the ammonium carbamate and to discharge the excess ammonia, along with the ammonia and carbon dioxide from the decomposed ammonium carbamate, as a gas stream from the high-pressure stripper. Ammonia, too, can be used here as a stripping gas. The gas stream from the high 20 pressure stripper is partly condensed in the high-pressure condenser, to which a carbamate stream from the medium-pressure recovery section is also added. Subsequently, the gas/liquid stream from the high-pressure condenser is supplied to a high-pressure separator, the liquid fraction being returned to the reactor via an ejector. The gas from the high-pressure separator is passed to the medium-pressure recovery 25 section. A process known to one skilled in the art is to increase the capacity of existing processes by replacing those process items that form a bottleneck in the process with larger equipment items. An example of an equipment item which would need to be replaced by a larger unit is for example the urea reactor. Such a process is 30 described in for example EP-0751121-A1. This patent publication discloses that the capacity of a Snamprogetti Self-Stripping Process can be increased by adding a second reactor or by replacing the existing reactor with a larger reactor. A drawback of expanding the reactor in this manner is that the costly high-pressure ammonia pumps also need to be replaced by larger pumps when the 35 original process conditions are maintained. The condenser and the stripper, too, will -2 Probably need to be replaced by units having a higher capacity. The drawback of replacing the reactor and high-pressure ammonia pumps is that high costs are involved. The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof. The aim of the invention is to develop a process for increasing the capacity of a urea process whereby replacement of costly equipment is avoided as much as possible. This is achieved by " the N/C ratio in the reactor being between 2.8 and 3.3 mol/mol, " the pressure in the high-pressure section of the process being between 13.5 and 16.0 MPa, e at least a portion of the process stream from the reactor being stripped in a CO2 stripper in which the process stream from the reactor is stripped by supplying heat and with the aid of carbon dioxide as stripping gas and e the condensing capacity in the high-pressure section of the process being increased. The N/C ratio is the molar ratio between ammonia (N) and carbon dioxide (C) in the reactor. In the existing urea process, this ratio was between 3.0 and 4.0 mol/mol. One measure taken to increase the capacity of the existing process is to lower the N/C ratio to a value between 2.8 and 3.3 mol/mol. In the existing urea process the pressure in the high-pressure section of the process was between 15.0 and 16.5 MPa. In increasing the capacity of the existing urea process, this pressure is reduced to a pressure of between 13.5 and 16.0 MPa. SPEC-800457 -2a in increasing the capacity, a third requirement is that the process stream from the reactor, comprising urea, ammonia, carbon dioxide, water and ammonium carbamate, be at least partly stripped in a CO 2 stripper, in which the process stream from the reactor Is stripped by supplying heat and with the aid of carbon dioxide as stripping gas. In the existing process this implies that a C02 stripper is added. The increased-capacity process then comprises a thermal stripper or an ammonia stripper as well as a C02 stripper in which a portion of the process stream from the reactor is stripped. One skilled in the art can readily control the optimum distribution of the process stream among the two types of stripper. It is also possible to convert the existing thermal stripper or ammonia stripper into a CO 2 stripper whereby the whole process stream from the reactor Is SPEC-800457 WO 2006/061083 PCT/EP2005/012201 -3 stripped in a C02 stripper. The existing thermal stripper or ammonia stripper can, of course, also be replaced with a new C02 stripper. The option to be chosen by one skilled in the art is dictated by the condition of the existing thermal stripper or ammonia stripper, bearing in mind that, in increasing the capacity, replacing high-cost 5 equipment is avoided wherever the equipment is in good physical condition. However, on account of the technical simplicity of the process it is preferable to strip the whole gas stream from the reactor in a C02 stripper. A fourth requirement for increasing the capacity of an existing urea process is to increase the condensing capacity in the high-pressure section of the 10 process. This can be accomplished in various ways. For example, it is possible to add a high-pressure scrubber or a second high-pressure condenser. Alternatively, it is possible to increase the condensing capacity of the existing condenser. The off-gases from the condenser are at least partially condensed in the high-pressure scrubber. 15 The high-pressure scrubber can be designed in two ways: 1: Substantially complete scrubbing of ammonia and carbon dioxide from the off-gas to be achieved by cooling with the aid of a heat exchanger followed by scrubbing with a medium-pressure carbamate solution. 2: Partial scrubbing of ammonia and carbon dioxide from the off-gas, with the 20 ammonia and carbon dioxide only being condensed in a heat exchanger. In this design, the carbamate solution originating from a medium-pressure recovery section is supplied to the high-pressure scrubber and/or the high-pressure condenser. For increasing the condensing capacity it is also possible to add a 25 high-pressure condenser in which the off-gases from the existing high-pressure condenser are condensed in a carbamate stream supplied from the medium-pressure recovery section to the additional high-pressure condenser. The high-pressure condenser to be added can be designed as a falling-film condenser or as a kettle type condenser. 30 The added high-pressure condenser may be arranged in parallel with or in series with the existing high-pressure condenser. Steam or hot water may be generated in the additional high-pressure condenser. When the added high-pressure condenser is arranged in parallel the off-gas stream from the stripper and the carbamate stream from the medium-pressure recovery section are split and directed to 35 both high-pressure condensers. The carbamate stream that is formed in the high- WO 2006/061083 PCT/EP2005/012201 -4 pressure condensers is returned to the reactor and the off-gases from the high pressure condensers are directed to the medium-pressure recovery section. In the series arrangement the off-gas from the existing high-pressure condenser is condensed in the added high-pressure condenser, with at least a portion 5 of the carbamate stream from the medium-pressure recovery section being supplied to the added high-pressure condenser. The carbamate stream from the added high pressure condenser can be supplied to the existing high-pressure condenser either separately or together with a portion of the carbamate stream from the medium pressure recovery section. The carbamate stream from the existing high-pressure 10 condenser is returned to the reactor and the off-gases from the high-pressure condensers are discharged to the medium-pressure recovery section. It is also possible to combine the carbamate streams from both high-pressure condensers and to return them, optionally via a separator, to the reactor. Preferably, the condensers are installed at a low elevation (near the 15 ground). Such installation requires the use of ammonia-driven ejectors. For increasing the capacity of the existing urea process still further it is preferred to increase the reaction capacity of the existing process also. This can be accomplished by, for example, by increasing the reaction volume of the existing reactor. 20 It is known to those skilled in the art that in a urea process the condensing capacity and the reaction capacity can be increased at the same time by adding equipment to the high-pressure section of the process in which condensation and reaction can be carried out simultaneously. Examples of such equipment are a pool condenser, a pool reactor 25 and a combi-reactor. The pool condenser is disclosed in for example EP-0155735-Al. The pool condenser can be installed horizontally or vertically. In the pool condenser, the off-gas from the stripper(s) is condensed and, additionally, a portion of the quantity of urea to be produced is formed in the pool condenser. The liquid stream that is passed 30 from the pool condenser to the existing reactor thus comprises both carbamate and urea. The pool reactor is disclosed in for example US-A-5767313. The pool reactor comprises a condenser section and a reactor section in an apparatus placed in horizontal position. 35 The combi-reactor is disclosed in for example US-B1 -6392096, in -5 US-B2-6680407 and in US-A-5936122. The combi-reactor comprises a condenser section and one or two reactor sections in an apparatus placed in vertical position. The condenser section may be placed above or below the reactor section. If two reactor sections are present, the condenser section is located between the two reactor 5 sections. In the pool reactor or the combi-reactor the off-gas from the stripper(s) is condensed in the condenser section, whereupon urea is formed in the reactor section or the reactor sections. At least a portion of the carbamate stream from the medium-pressure recovery section is supplied to the condenser section of the pool 10 reactor or combi-reactor. The process stream from the reactor section is passed to the C02 stripper and optionally the thermal or ammonia stripper. A pool reactor and a combi-reactor may also be used for replacing the existing reactor and condenser. The invention also relates to a urea plant comprising, in the high 15 pressure section of the process, a reactor, a thermal stripper or an NH3 stripper and a condenser, in which, besides the thermal stripper or NH 3 stripper, a C02 stripper Is also present in the high-pressure section of the process. The urea plant may also comprise a high-pressure scrubber or a second condenser if the condensing capacity in the high-pressure section of the 20 process has been increased If both the condensing capacity and the reaction capacity in the high pressure section of the process have been increased, the urea plant may comprise a pool condenser, a pool reactor or a combi-reactor. The invention also comprises a urea plant comprising, in the high 25 pressure section of the process, a pool reactor or a combi-reactor, a thermal stripper or an NH 3 stripper and a C02 stripper. The invention also relates to a process for increasing the capacity of an existing urea process comprising, in the high-pressure section of the process, a reactor in which carbon dioxide and ammonia react to form urea, a thermal stripper in which the process stream from the reactor is stripped by supplying heat or an ammonia stripper in which the process stream from the reactor is stripped by supplying heat with the aid of ammonia as stripping gas and a condenser in which the stripping gases are condensed, whereupon the condensate formed is returned to the reactor, wherein - the N/C ratio in the reactor is between 2.8 and 3.3 mol/mol, - the pressure in the high-pressure section of the process is between 13.5 and 16.0 MPa, SPEC-800457 -5a - at least a portion of the process stream from the reactor is stripped in a C02 stripper in which the process stream from the reactor is stripped by supplying heat and with the aid of carbon dioxide as stripping gas and - the condensing capacity in the high-pressure section of the process is 5 increased. The invention also relates to a urea plant comprising a high pressure scrubber and, in the high-pressure section of the process, a reactor, a thermal stripper or an NH 3 stripper and a condenser, wherein, besides the thermal stripper or NH 3 , stripper, a CO 2 stripper is present in the high-pressure section of the 10 process. The invention also relates to a urea plant comprising, in the high pressure section of the process, a pool reactor or a combi-reactor, a thermal stripper or an NH 3 stripper and a C02 stripper. The invention is elucidated with reference to the following examples without being limited thereto. Figure 1 represents the Snamprogetti Self-Stripping Process according to the state of the art. In a reactor (R) ammonia and carbon dioxide are contacted at a pressure of 15 MPa at an N/C ratio of 3.5 mol/mol. The process stream from the reactor is directed to a stripper (S) in which the process stream from the reactor is stripped with the aid of heat. Subsequently, the urea-containing process stream from the stripper is passed to the medium-pressure recovery section (MP) in which this process stream is recovered further and in which process a carbamate SPEC-8O0457 WO 2006/061083 PCT/EP2005/012201 -6 stream is formed. In addition, a gaseous stream is separated in the medium-pressure recovery section, which stream is directed to a section (N) in which ammonia gas is recovered. This ammonia gas is returned to the reactor (R) via the ejector (E). The urea-containing stream passes from the medium-pressure recovery section to a low 5 pressure recovery section (LP). On leaving the low-pressure recovery section, the urea stream (U) is concentrated and recovered further. The carbamate stream from the low-pressure recovery section is returned to the medium-pressure recovery section. The stripping gases from the stripper are mixed in mixer (M), together 10 with the carbamate stream from the medium-pressure recovery section and are directed to the condenser (C). Here, the stripping gases are partly condensed. The gas/liquid stream from the condenser is supplied to a separator (A). The liquid fraction is returned from the separator to the reactor by means of the ejector (E) which is driven by the ammonia feed. The gas stream from the separator passes to the 15 medium-pressure recovery section. The capacity of a process according to figure 1 is 1550 tonnes/day. Figure 2 represents a Snamprogetti Self-Stripping Process with increased capacity according to the invention. In a reactor (R), whose reaction volume has been increased, ammonia and carbon dioxide are contacted at a pressure of 14.0 20 MPa at an N/C ratio of 3.0 mol/mol. The process stream from the reactor is directed to the strippers (Sn and Sb). In the stripper (Sb) the process stream from the reactor is stripped with the aid of heat and in the stripper (Sn) with the aid of heat and with carbon dioxide as stripping gas. Subsequently, the urea-containing process stream from the stripper (Sb) passes to the medium-pressure recovery section (MP) in which 25 this process stream is recovered further, whereby a carbamate stream is formed. The urea-containing process stream from the stripper (Sn) passes to a newly installed low-pressure recovery section (LPn), in which this process stream is recovered further, whereby a low-pressure carbamate stream is formed. Additionally, in the medium-pressure recovery section a gaseous stream is separated, which is 30 directed to a section (N) in which ammonia gas is recovered. This ammonia gas is returned to the reactor (R) via the ejector (E). The urea-containing stream is also directed from the medium-pressure recovery section to the low-pressure recovery section (LPb). On leaving the low-pressure recovery sections (LPb and LPn), the urea streams (U) are concentrated and recovered further. The carbamate streams from the 35 low-pressure recovery sections are returned to the medium-pressure recovery section.

WO 2006/061083 PCT/EP2005/012201 -7 The stripping gas from the stripper (Sb) passes to the condenser (C). A portion of the carbamate stream from the medium-pressure recovery section may optionally be added to the condenser. The stripping gases are partially condensed in the condenser. The non-condensed gases are directed from the condenser to the 5 scrubber (SC). The stripping gas from stripper (Sn) and the off-gas from the reactor are also directed to scrubber (SC). In the scrubber practically all gases are condensed in the carbamate stream from the medium-pressure recovery section, which stream is also supplied to the scrubber. The condensate returns to the reactor via ejector (E). Waste gases (a), containing traces of ammonia and carbon dioxide, are discharged 10 from the scrubber to an absorber. The capacity of a process according to figure 2 is 2400 tonnes/day. Figure 3 represents a Snamprogetti Self-Stripping Process with increased capacity according to the invention. In a reactor (R), whose reaction volume has been increased, ammonia and carbon dioxide are contacted at a pressure of 14.0 15 MPa at an N/C ratio of 3.0 mol/mol. The process stream from the reactor is directed to the strippers (Sn and Sb). In the stripper (Sb) the process stream from the reactor is stripped with the aid of heat and in the stripper (Sn) with the aid of heat and with carbon dioxide as stripping gas. Subsequently, the urea-containing process stream from the stripper (Sb) passes to the medium-pressure recovery section (MP) in which 20 this process stream is recovered further, whereby a carbamate stream is formed. The urea-containing process stream from the stripper (Sn) passes to a newly installed low-pressure recovery section (LPn), in which this process stream is recovered further, whereby a low-pressure carbamate stream is formed. Additionally, in the medium-pressure recovery section a gaseous stream is separated, which is 25 directed to a section (N) in which ammonia gas is recovered. This ammonia gas is returned to the reactor (R) via the ejector (E). The urea-containing stream is also directed from the medium-pressure recovery section to the low-pressure recovery section (LPb). On leaving the low-pressure recovery sections (LPb and LPn), the urea streams (U) are concentrated and recovered further. The carbamate streams from the 30 low-pressure recovery sections are returned to the medium-pressure recovery section. The stripping gas from the strippers (Sn and Sb) passes to the condensers (Cn and Cb). A portion of the carbamate stream from the medium pressure recovery section may optionally be added to the condenser (Cb). The stripping gases are partially condensed in the condensers. The non-condensed gases 35 are directed from the condensers (Cn and Cb) to the scrubber (SC). The off-gas from WO 2006/061083 PCT/EP2005/012201 -8 the reactor is also directed to scrubber (SC). In the scrubber practically all gases are condensed in the carbamate stream from the medium-pressure recovery section, which stream is also supplied to the scrubber. The condensate returns to the reactor via ejector (E). Waste gases (a), containing traces of ammonia and carbon dioxide, 5 are discharged from the scrubber to an absorber. The capacity of a process according to figure 3 is 2400 tonnes/day. Figure 4 represents a Snamprogetti Self-Stripping Process with increased capacity according to the invention. In a reactor (R), whose reaction volume has been increased, ammonia and carbon dioxide are contacted at a pressure of 14.0 10 MPa at an N/C ratio of 3.0 mol/mol. The process stream from the reactor is passed to the stripper (Sn). In the newly added stripper (Sn), which replaces the existing stripper, the process stream from the reactor is stripped with the aid of heat and with carbon dioxide as stripping gas. The urea-containing process stream from the stripper is then directed to the medium-pressure recovery section (MP) in which this process stream is 15 recovered further, whereby a carbamate stream is formed. In the medium-pressure recovery section a gaseous stream is also separated, which stream passes to a section (N) in which ammonia gas is recovered. This ammonia gas returns to the reactor (R) via ejector (E). The urea-containing stream is directed from the medium-pressure recovery section to the low-pressure 20 recovery section (LP). On leaving the low-pressure recovery section, the urea stream (U) is concentrated and recovered further. The carbamate stream from the low pressure recovery section is returned to the medium-pressure recovery section. The stripping gas from the stripper (Sn) is supplied to the newly installed pool condenser (PC), which replaces the existing condenser. A portion of the 25 carbamate stream from the medium-pressure recovery section may optionally be added to the pool condenser. The stripping gases are partially condensed in the pool condenser. The non-condensed gases are directed from the pool condenser to the scrubber (SC). The reactor off-gas is also directed to scrubber (SC). In the scrubber, practically all gases are condensed in the carbamate stream from the medium 30 pressure recovery section, which stream is also supplied to the scrubber. Waste gases (a), containing traces of ammonia and carbon dioxide, are discharged from the scrubber to an absorber. The condensate returns to the pool condenser. The condensate that forms in the pool condenser is returned to the reactor via the ejector (E). 35 The capacity of a process according to figure 4 is 2610 tonnes/day.

WO 2006/061083 PCT/EP2005/012201 -9 Figure 5 represents a Snamprogetti Self-Stripping Process with increased capacity according to the invention. In a reactor (R), whose reaction volume has been increased, ammonia and carbon dioxide are contacted at a pressure of 14.0 MPa at an N/C ratio of 3.0 mol/mol. The process stream from the reactor is passed to 5 the stripper (Sn). In the newly installed stripper (Sn), which replaces the existing stripper, the process stream from the reactor is stripped with the aid of heat and with carbon dioxide as stripping gas. The urea-containing process stream from the stripper is then directed to the medium-pressure recovery section (MP) in which this process stream is recovered further, whereby a carbamate stream is formed. 10 In the medium-pressure recovery section a gaseous stream is also separated, which stream passes to a section (N) in which ammonia gas is recovered. This ammonia gas returns to the reactor (R) via ejectors (El and E2). The ammonia gas can be heated before it enters ejector (El) and/or (E2). The urea containing stream is directed from the medium-pressure recovery section to the low-pressure 15 recovery section (LP). On leaving the low-pressure recovery section, the urea stream (U) is concentrated and recovered further. The carbamate stream from the low pressure recovery section is returned to the medium-pressure recovery section. A portion of the stripping gas from the stripper (Sn) is directed to the newly installed pool condenser (PC), which replaces the existing condenser. A portion 20 of the carbamate stream from the medium-pressure recovery section may optionally be added to the pool condenser. The stripping gases are partially condensed in the pool condenser. The non-condensed gases are passed from the pool condenser to the scrubber (SC). The reactor off-gas is also directed to scrubber (SC). In the scrubber, practically all gases are condensed in the carbamate stream from the medium 25 pressure recovery section, which stream is also added to the scrubber. Waste gases (a), containing traces of ammonia and carbon dioxide, are discharged from the scrubber to an absorber. The condensate is returned to the pool condenser. The condensate that forms in the pool condenser is returned to the reactor via the ejector (El). 30 Another portion of the stripping gas from the stripper (Sn) is returned directly from the stripper to the reactor via an ejector (E2). This design allows the carbon dioxide to be added as much via the stripper as possible, as a result of which a lower steam consumption is achieved. The capacity of a process according to figure 5 is 2610 tonnes/day. 35

Claims

1. Process for increasing the capacity of an existing urea process comprising, in the high-pressure section of the process, a reactor in which carbon dioxide and ammonia 5 react to form urea, a thermal stripper in which the process stream from the reactor is stripped by supplying heat or an ammonia stripper in which the process stream from the reactor is stripped by supplying heat with the aid of ammonia as stripping gas and a condenser in which the stripping gases are condensed, whereupon the condensate formed is returned to the reactor, wherein 10 - the N/C ratio in the reactor is between 2.8 and 3.3 mol/mol, - the pressure in the high-pressure section of the process is between 13.5 and 16.0 MPa, - at least a portion of the process stream from the reactor is stripped in a CO 2 stripper in which the process stream from the reactor is stripped by supplying heat and with the 15 aid of carbon dioxide as stripping gas and - the condensing capacity in the high-pressure section of the process is increased.

2. Process according to claim 1, wherein the whole process stream from the reactor is stripped in a CO 2 stripper. 20

3. Process according to claim 1 or 2, wherein the condensing capacity is increased by adding a high-pressure scrubber to which the off-gases from the condenser and optionally a medium-pressure carbamate stream are supplied. 25

4. Process according to any one of claims 1-3, wherein the condensing capacity is increased by adding a second high-pressure condenser.

5. Process according to any one of claims 1-4, wherein, in addition, the reaction capacity is increased by increasing the reaction volume of the reactor. 30

6. Process according to either of claims 1-2, wherein the condensing capacity and the reaction capacity are increased by adding, to the high-pressure section of the process, a pool condenser, a pool reactor or a combi-reactor to which the off-gases from the stripper(s) and a medium-pressure carbamate stream are supplied. 35 SPEC-600457 -11

7. Process according to either of claims 1-2, wherein the condensing capacity and the reaction capacity are increased by replacing the existing reactor and condenser with a pool reactor or a combi-reactor. 5

8. Urea plant comprising a high-pressure scrubber and, in the high-pressure section of the process, a reactor, a thermal stripper or an NH 3 stripper and a condenser, wherein, besides the thermal stripper or NH 3 , stripper, a C02 stripper is present in the high-pressure section of the process. 10

9. Urea plant according to claim 8, wherein the plant comprises, in the high-pressure section of the process, a second condenser.

10. Urea plant according to claim 8, wherein the plant also comprises, in the high pressure section of the process, a pool condenser, a pool reactor or a combi-reactor. 15

11. Urea plant comprising, in the high-pressure section of the process, a pool reactor or a combi-reactor, a thermal stripper or an NH 3 stripper and a C02 stripper.

12. Process according to claim 1, substantially as hereinbefore described with reference 20 to any one of Figures 2-5.

13. Urea plant according to claim 8 or claim 11, substantially as hereinbefore described with reference to any one of Figures 2-5. SPEC-800457