JPS605521B2 - How to reuse condensed water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an economical method for reusing condensed water produced by lowering the temperature of a mixed gas during the purification process of a mixed gas obtained by subjecting hydrocarbons to steam.

There are many chemical plants that purify the pooled gas obtained by steam refining hydrocarbons to obtain useful products, or that synthesize useful substances using the purified gas as a raw material.

That is, in the first stage, hydrocarbons such as natural gas, naphtha, and heavy oil are converted into methane, hydrogen,
A high-temperature mixed gas containing carbon monoxide is obtained, which is purified in a subsequent stage to produce fuel gas, pure hydrogen or ammonia,
Synthetic raw material gases such as methanol are produced. In these chemical plants, the high-temperature mixed gas obtained in the first stage contains a considerable amount of water vapor, and as there is a process in which the temperature drops in the subsequent purification process, the water vapor in the mixed gas becomes condensed water and is separated. do.

The economical reuse of this condensate reduces energy and water
This is an important issue in improving the balance of water vapor and other resources. On the other hand, these chemical plants use many far-D compressors and pumps in the plant, but the drive of these rotating machines is becoming more and more like a steam turbine, so a high-pressure steam generation system is installed. A steam system is installed in which the generated high-pressure steam is passed through a steam turbine and expanded, and the condensed water is circulated through the high-pressure steam generation system, where it is converted into high-pressure steam along with highly treated water newly supplied from outside the system.

At this time, a portion of the high-pressure steam is extracted as medium-pressure steam, a portion of which is supplied as steam for producing mixed gas, and the remainder is further introduced into another steam turbine for expansion and condensation. . Conventionally, the condensed water from the mixed gas is either discarded or subjected to complicated purification treatment and then introduced into the high-pressure steam generation system for reuse, thereby reducing the amount of highly treated water newly supplied from outside the system. method has been implemented.

In the former case, disposing of condensed water poses problems in terms of environmental protection, so the conventional method has been to perform a complicated purification process and then introduce it into a high-pressure steam generation system. Therefore, as described below, it has the disadvantage of requiring extremely high-level purification processing.Condensed water contains ammonia, carbon dioxide, methanol, and other harmful gases as well as metal compounds, and cannot be supplied as is. is unsuitable for high-pressure steam generation systems.For this reason, deaeration using steam, the so-called steam stripping method, has been implemented as a purification process.However, this method alone cannot
Deposition of foreign matter and corrosion tend to occur in turbine blades and turbine condensers, and in high-pressure steam generating boilers, foaming tends to be severe, so purification is insufficient. In recent years, combination treatments such as steam stripping and ion exchange, Oku resin treatment, and activated carbon treatment have been implemented, making them suitable for high-pressure steam generation systems, but they require a lot of equipment and operation processes, which only increases costs. However, there are also drawbacks such as the growth of algae on ion exchange resins. The present invention provides a method for reusing condensed water by simply subjecting it to steam stripping or aeration treatment without performing the conventional complicated purification treatment.

That is, in this invention, after subjecting the condensed water to steam stripping or aeration, it is introduced into a separately provided medium pressure steam generator to generate medium pressure steam, which is then recycled as part of the reforming steam. It is something to be used.
This invention relates to a gasification process in which hydrocarbons are steam-reformed at medium pressure to produce a mixed gas, a purification process of the mixed gas, and a process for medium-pressure steam obtained by expanding high-pressure steam from a high-pressure steam generation system. In the production of purified gas, which consists of the step of using a part of the gas as waste steam in the gasification step, the condensed water generated by cooling the mixed gas in the refining step is subjected to steam stripping or aeration treatment, and then separately provided. It is to reuse it as medium pressure steam in a medium pressure steam generator as part of the reforming steam in the gasification process.

However, medium pressure and high pressure are comparative expressions, and do not indicate specific pressures. Medium pressure is the pressure at which steam reforming is carried out, usually 5 to 70 kg', and high pressure is the pressure at which steam reforming is carried out. It refers to a pressure higher than the medium pressure of , usually 60 to 150
kg'. The present invention will be explained in detail below using an example of an ammonia production plant. Raw material hydrocarbons such as natural gas or naphtha in the 40k9' area introduced from the conduit 11 are mixed with water vapor in the 40k9' area from the conduit 25 and the conduit 1.
It is mixed with 40k9/ground steam from No. 2 and introduced into the furnace tube 1 of the primary steam reforming furnace through the conduit 13.

The high-temperature mixed gas generated by reforming in the furnace tube 1 at 33 [9/ ground] is introduced into the second political furnace 2 via the conduit 14.
The high temperature mixed gas containing hydrogen and carbon monoxide produced by reacting with the air from the conduit 15 is cooled through the conduit 16, heat exchanger 3, conduit 17, heat exchanger 4, conduit 18, and heat exchanger 5. , from the conduit turtle 9 to the separator 6, where it is separated from the condensed water and taken out from the conduit 21, and then, although not shown, CO
It is compressed to 300k9' through a conversion and methanator step, and is led into an ammonia synthesizer, where ammonia is synthesized. On the other hand, the condensed water is introduced into the deaerator 7 via the conduit 20. The condensed water is here degassed with water vapor from conduit 26, i.e. most of the dissolved ammonia, carbon dioxide, methanol and other harmful gases are removed, and is taken out from conduit 22, while the treated condensed water is removed from conduit 23. ,24
The generated medium pressure steam is then passed through a conduit 25 and mixed with the raw material hydrocarbon. On the other hand, 100 kg' of high-pressure steam from the high-pressure steam generator 30 is introduced into the steam turbine 31 through a conduit 37, a part of which is taken out as medium-pressure steam of 40k9', and further through a conduit 38. A portion is mixed with the feedstock hydrocarbon via conduit 12, and the remainder is mixed with the steam turbine 32.
, 33 and led to the condenser 35 via conduits 39, 40, 41. On the other hand, the steam expanded to a low pressure by the steam turbine 31 is guided to the condenser 35 via a conduit 42 via a heat exchanger 34. Condenser 35 receives newly supplied highly treated water from outside the system based on the internal mass balance through conduit 4.
Supplied from 3. The condensate is led to three high-pressure steam generators via a conduit 44, a pump 36, and a conduit 45, and high-pressure steam is generated. In the above process, harmful gases such as ammonia and carbon dioxide contained in the condensed water from the separator 6,
Most of methanol, methylamine, formic acid, formaldehyde, etc. are removed by a simple degassing device 7, and even if some harmful gases remain, the condensed water containing them will not have any adverse effect on the equipment. Medium pressure steam generator 8
At the same time, the remaining part of the harmful gas is introduced into the furnace tube 1 of the primary steam reforming furnace, where the harmful gas is decomposed. Incidentally, metals or their compounds in the condensed water can be prevented from accumulating by flowing appropriately as in a normal medium-pressure steam generator. As can be seen from the above description, the method of the present invention has two advantages over methods that do not reuse condensed water: first, it has a deaeration device that allows easy reuse of condensed water and a small-capacity medium-pressure steam generator. Second, newly supplied highly treated water, so-called pure water, which is supplied to the high-pressure steam generation system from outside the system, is saved by the amount of reused condensed water.The amount of purified water saved is, for example, In the conventional method in which condensed water is not reused in the ammonia production plant, the amount of pure water supplied from outside the system was 7.3 tons per ton of ammonia, but in this invention, only 6.1 tons of pure water is supplied. , 1.2 tons of pure water will be saved per 1 ton of ammonia.For an ammonia factory with a capacity of 1000 tons per day, the savings will be enormous.

In addition, compared to the conventional method, which involves complex treatment of condensed water, i.e., ion exchange resin treatment, steam aeration, oxidation, activated carbon treatment, and ion exchange resin treatment, the savings in pure water is the same. However, the method of the present invention requires only a simple deaerator and a small-capacity medium-pressure steam generator, and can be operated for a long period of time without causing any problems. The above explained the case of ammonia synthesis, but
This invention consists of a first process that requires steam at medium pressure and high temperature, such as methanol synthesis and hydrogen production, and then a second process that purifies the mixed gas from the previous process and generates high-pressure steam at a higher pressure than the first process. The present invention can be widely applied to plants having a steam system having an apparatus and a steam turbine for expanding the high-pressure steam without departing from the invention.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of an embodiment of the method of this invention. Figure 1

Claims (1)

[Claims] 1 A gasification process in which hydrocarbons are reformed with steam at medium pressure to produce a mixed gas, a process for generating the mixed gas, and a part of the medium-pressure steam obtained by expanding high-pressure steam from a high-pressure steam generation system. In the production of purified gas, which comprises a step of using it as reforming steam in the gasification step, the condensed water generated by cooling the mixed gas in the purification step is subjected to steam stripping or aeration treatment, and then separately Condensation characterized in that the amount of reforming steam from the high-pressure steam generation system is reduced by converting the intermediate-pressure steam into intermediate-pressure steam in the provided intermediate-pressure steam generator and reusing it as reforming steam in the gasification step. How to reuse water.