The function of high-pressure flashing

There are two functions: one is to release gases dissolved in water, either to recover them or to discharge them； Second is the recovery of heat, using flash steam to heat the recycled graywater.

Gases in the dissolved water evaporate, producing steam

This post was last edited by GSP on 2013-3-16 at 22:33. The use of flash evaporation is intended to separate gases from dissolved water, while high pressure is utilized to recover sensible heat energy

High-pressure flash vaporization feedstock is originally a mixture of vapor, gas, and water that has been condensed and contains a certain amount of heat; it basically contains no solid impurities. Is the statement that high-pressure flash vaporization has only one… (I’m not sure if this expression is accurate?) The purpose is to remove non-condensable gases; the high pressure is used to retain the majority of the heat for use in subsequent stages, with most of this heat being supplied to the deoxidation tank as needed! This is just my personal understanding; I hope the teachers will point out any mistakes This post was last edited by GSP on 2007-12-24 14:27]

Basically, I agree with what was said on the 6th floor too! Its main function is to flash out the gases dissolved in the greywater! And low-flash and vacuum flash are used to mainly recover heat and separate solid impurities!

Currently, high-pressure and multi-nozzle gasification furnaces mostly use evaporative hot water towers to replace high-pressure flash tanks, and I believe this replacement is quite valuable. The evaporative hot water tower is divided into an evaporation chamber and a hot water chamber; it separates the acidic gases that are difficult to remove from the cooled syngas, while also recovering the remaining heat from the cooled syngas – achieving two goals at once, so why not do it?

The ash water treatment stage in coal water slurry gasification involves separating the ash residues from the high-pressure black water at lower temperatures and normal pressure, through processes such as flocculation, sedimentation, and filtration; this requires steps for reducing pressure, cooling down the water, and removing the combustible and toxic gases dissolved in it； The water removed during the degassing process should be recovered into the process system as much as possible, in order to minimize the amount of water that needs to be added from outside ； At the same time, the treated graywater under normal pressure, as well as the fresh water added from the outside, may contain dissolved oxygen; therefore, a heating and deoxygenation process is required before it is returned to the high-pressure system ； The deoxygenated gray water needs to have its temperature increased as much as possible before being returned to the high-pressure system, in order to reduce heat loss from the crude syngas and to maintain a high water vapor ratio in the crude syngas, which facilitates the subsequent conversion process. On the surface, high-pressure flashing appears to be merely one step in the processes of pressure reduction, temperature lowering, and degassing; however, upon closer examination, it is clear that Texaco’s staged flashing process represents the best solution that takes into account all of these various process requirements. The flash evaporation process enables the reduction of pressure, cooling, and degassing to take place; at the same time, it generates a large amount of process steam, which serves as the heat source required in the latter two conditions. As the process medium is heated, the large amount of water present in the gas is condensed, and after separation it is returned to the process system, thereby reducing water loss in the system. By taking another look at the temperatures under the last two operating conditions and the heat sources required, it becomes easy to understand the rationale behind setting the high-pressure and low-pressure flash pressures. Let’s start with the deoxygenation process. The operating temperature of the deoxygenator is around 108 degrees Celsius; the heating medium is used to heat the clarified graywater as well as the condensate returned from various processes to this temperature, thereby enabling deoxygenation. This requires the temperature of the process steam to be higher than this value, and the pressure to be sufficient to overcome the pressure drop in the piping system and equipment; thus, a low-pressure flash pressure of around 3 bar is determined ； Then, based on the heat required for heating and deoxygenation, the amount of steam needed for the low-pressure flash process is determined, thereby fixing the pressure for high-pressure flashing at around 8 bar ； The process steam generated by high-pressure flashing is entirely used to heat the graywater that returns to the high-pressure system, thus making full use of it. The moisture in the steam from the low-pressure flash process condenses during the heating and deoxygenation process, and returns directly to the graywater system in the deoxygenation tank ； In the high-pressure flash process, most of the steam used for heating high-pressure graywater condenses, and after separation, it can also be returned to the process system. Vacuum flash evaporation can further achieve cooling and degassing effects; however, due to its relatively low temperature and the limited amount of heat that can be recovered, no heat recovery system was implemented. Instead, cooling water is used for condensation, with the resulting condensate being returned to the system for reuse. Such a complex graywater treatment system makes full use of the heat contained within the high-pressure black water itself, without relying on any external heat sources such as steam; it makes rational use of this thermal energy through staged flashing, thereby meeting all the process requirements while minimizing the amount of cooling water needed. It also maximizes the reuse of process water, thus achieving both energy savings and environmental protection – truly a classic example of excellent process design. Last edited by bone on 2007-12-27 12:57]

I’ve learned something – BONExx’s posts are really informative. I’m not sure what Shell’s graywater treatment process is like

Are the furnaces with multiple nozzles used in China also operated using this same process? Last edited by wildhalf on 2007-12-25 09:24]

Both the Northwest Institute and East China University of Science and Technology \"continue to use\" this graywater treatment process, while Shell employs external steam stripping for degassing; the design of its process is not particularly sophisticated. Fortunately, Shell generates less amount of graywater, so its impact on the overall energy consumption of the facility is not significant.

Currently, graywater flash evaporation systems are designed with either two or four stages, mainly due to differences in vaporization pressure. What is everyone’s experience in this regard? How to consider it?

Divided into 2-stage flash, 3-stage flash, and 4-stage flash. Last edited by Langtaosha on 2008-3-17 16:57.]

The main functions of high-pressure flashing are to lower the temperature of the black water, concentrate the solid content in it, remove a small amount of acidic gases, and recover heat

Bone not only has a high level of technical skill but also excellent literary talent

Bone** – if you could provide an analysis of the differences and advantages between multi-stage flashing and steam stripping using external steam, it would help to better illustrate the sophistication of GE’s three-stage flashing design. Looking forward to Bone’s excellent work.

I also understood the fixed-bed version; it’s well-organized

I disagree with this view; Shell’s stripping process makes use of its own flashing, as well as the steam generated by the process itself as the stripping steam, while any excess low-pressure steam is sent outside.

It’s okay if you don’t agree; different opinions are welcome. I hope the person who posted above can provide a detailed analysis to support their view, rather than just presenting one opinion. Another point is that although the steam used for stripping is steam generated as a by-product of the gasification unit, it is undeniable that it reduces the amount of energy that the gasification unit can supply externally. It does not matter whether this steam comes from the gasification unit or from an external pipeline network; what is important is that, compared to the graywater system, this heat needs to be supplied from outside, as it cannot be provided by the waste heat from the process itself.

Bone said it very well; I agree.