When feeding the sludge pool water into the vacuum flash tank, is it better to do so below the liquid level or above it?

Firstly, 0.25 MPa cannot be called vacuum flash evaporation; I believe it is better for the sludge pond water to enter from the upper part of the vacuum flash evaporation tank, as this water still needs to undergo flash evaporation, and its temperature is sometimes relatively high as well.

Since it’s going to flash evaporation, feeding from the top is necessary; otherwise, what’s the use of injecting water from the sludge tank? ? Also, it seems that the original poster’s question is referring to two different things (that’s how I understand it), right? On forums, to get satisfactory answers or insights, you need to clarify your question! Looking at the topic again, I understand now: you mean that one stream is the black water coming from the sludge tank, and the other is the black water resulting from high-flash and low-flash processes. It’s certain that in both cases, the water enters from the top. Although the black water in the slag pool contains very little non-condensable gas, it has a relatively high content of fine ash, and therefore also requires flash evaporation for concentration. Let’s listen to the experts’ opinions together again.

I agree with GSP’s opinion

The key is that the water coming from the slag pool isn’t that hot – can it flash vaporize? Take a look at the piping layout of your own device and think about it again – what the original poster said does make sense.

With your reminder, it makes sense – the sludge pool has a temperature of around 70 degrees, and vacuum flash evaporation takes place at around 60 degrees; the black water is fed into the vacuum system from the bottom. It would be better for this black water to go directly into the clarification and sedimentation equipment. It indeed seems unnecessary, but most designs follow this approach.

In my opinion, the addition of sludge water to the flash vessel serves two main purposes: firstly, it reduces the amount of vapor generated, thereby decreasing the demand for circulating water. The gray water coming in at 0.025 MPa has a temperature of around 127 degrees, while the sludge water has a temperature of about 60 degrees; it can be cooled directly. However, the current location where this water is added does not seem to allow for such cooling. I believe that the inlet for the sludge water should be placed after the angle valve； On the other hand, the fine ash content in the slag pool water is extremely low; entering the vacuum flasher dilutes the concentrated ash water, thereby reducing blockages in the liquid pipelines under vacuum conditions.

In my understanding, the water from the sludge tank is fed into the vacuum flasher not for flash evaporation purposes, but to create a vacuum before starting up the system; under normal conditions, this water can be directly sent to the clarification tank. ——Vacuum flash evaporation — Clarifier; Sludge tank water — { ————————Clarifier

During normal production, the water from the slag pool is sent to the vacuum flash tank to absorb the flash vapor generated from the ash water under low pressure; only when the furnace is heated to 800 degrees does the water from the slag pool go to the clarification tank

Upstairs, may I ask if the low-pressure flash vapor is sent to the vacuum system? We only know that the gas phase from low-pressure flashing is sent to the deoxygenation tank or the low-pressure flashing condenser. Furthermore, vacuum flash evaporation is not an absorption process. The purpose of flash evaporation is to take advantage of the fact that water has different boiling points at various pressures – the lower the pressure, the lower the boiling point. Using this principle, the gasified black water is cooled step by step, which facilitates the settlement of fine particles contained in it. By applying this principle to flash evaporate the gasified black water, the harmful gases present in it are removed.

The gas phase from low-pressure flashing is sent to the deoxygenation tank, while the liquid phase, being black water at 129 degrees, is sent for vacuum flashing

What the coal miner upstairs said is correct; it’s mainly to establish a circulation in the vacuum flash system in advance before starting the machine. As for other uses that can arise from designing such a pipeline, they are not primary, but it’s certainly possible to develop additional uses if utilized properly.

In Texaco’s technology, the black water from the slag tank is sent to a vacuum environment for flashing throughout the entire process, and this is independent of the startup process! In some designs, it is indeed the vacuum system that is used to establish the initial liquid level balance for the water during startup as well as while the system is in operation, but this applies only during the startup phase and has nothing to do with steady-state operation. The core issue now is whether to introduce it from the top or from the bottom. I support introducing it from the top, and there are two reasons for this: 1. It doesn’t matter whether flash evaporation takes place or not; at least it can remove some of the non-condensable gases dissolved within ； 2. It is mixed with the black water of low flash point to achieve the effect of concentrating and cooling the black water, thereby reducing its temperature and facilitating sedimentation. The temperature is a key factor determining the quality of black water sedimentation; ideally, this temperature should be around 45 degrees. This post was last edited by GSP on 2009-3-4 12:48 ]

After reading everyone’s opinions, I’d like to share some of my own thoughts. First and foremost, it’s clear that in the original Texaco technology package, the water from the sludge tank always had to flow into the vacuum flasher. Later on, due to the difference in pressure between the water from the sludge tank and that from low-pressure flashing, it became difficult to maintain the required pressure in the vacuum flasher. In the current Texaco technology package, this water from the sludge tank is directed directly to the sedimentation tank. The purpose of retaining the pipeline leading to the vacuum flasher is to establish liquid levels in both the upper and lower sections of the vacuum flasher when the ash treatment unit is started up. The sludge water is first introduced into the upper section; once its level reaches 50%, it is then sent to the lower section. When the level in the lower section also reaches 50%, the sedimentation tank feed pump is used to recycle the sludge water back to the upper section. Once the liquid levels in both sections are normal, the water from the sludge tank can again be directed back to the sedimentation tank. However, I once read in an old document that, in the company’s modifications to the graywater system, the water coming from the sludge tank and going to the vacuum flasher was directed to the low-pressure flasher, entering it at the lower part of the graywater pipeline. The reason for this was that the temperature of the water from the sludge tank was low; if it entered the vacuum flasher from the top, it would affect the flashing effect of the graywater coming from the low-pressure flasher, similar to the effect of spraying. Therefore, in my opinion, if the capacity of the sedimentation tank is not sufficient to meet the process requirements and the water from the sludge tank must pass through vacuum flash evaporation, it should enter the vacuum flash evaporator from the lower part of the pipeline supplying water for low-pressure flash evaporation, in order to avoid affecting the efficiency of vacuum flash evaporation. As someone upstairs said, even if not much flashing occurs, it’s still possible to remove some of the dissolved gases. If the sedimentation tank can meet the process requirements, it’s better to avoid using a vacuum flasher, as the pressures of the two feed streams are different, making it difficult to maintain a constant vacuum level in a vacuum flasher! If there are any mistakes, I hope experts will offer their criticism and suggestions!

Do you have a forced circulation pump in your low-pressure flash tank? It has a significant impact on the flashing effect.:) :)

It should be fed from the top; if the sedimentation tank is sealed and the graywater contains small amounts of acidic gases, etc., entrainment into the flash evaporator can remove these gases.

Can’t the feed at the lower part of the upper floor be flashed then?