Monotube Flash Boiler Design

[HMEL]

OK HMEL, you've peaked my curiosity,...what requirements are you referring to that would prevent the Osias fuel pump from pumping water??

Below is a drawing of the internal parts of these pumps. As you can see, they're tiny impellor-vane pumps, well suited to pump most any fluid.

My biggest question is, at what pressure will the Relief Valve open?

View attachment 151057

Well for one thing they are often buried in the fuel tank to keep them cool. Second the hot condensate is going to significantly heat that pump up. And because there is temperature not sure what the suction head requirement is enough for the service. And there is a possible issue with the seals in that service. Now I have not really looked at it from boiler feedpump specs but you will need an output of over 20% over flow rate at a pressure above your operating pressure. But assuming you have checked the specs and it complies there is still the issue of what appears to be a plastic housing which is ok for fuels not so for hot liquids. But you can always try it. So that is why I suggest you talk to the factory they may say yes or they may say no way will it work in that service.

 

[Toymaker]

Well for one thing they are often buried in the fuel tank to keep them cool. Second the hot condensate is going to significantly heat that pump up. And because there is temperature not sure what the suction head requirement is enough for the service. And there is a possible issue with the seals in that service. Now I have not really looked at it from boiler feedpump specs but you will need an output of over 20% over flow rate at a pressure above your operating pressure. But assuming you have checked the specs and it complies there is still the issue of what appears to be a plastic housing which is ok for fuels not so for hot liquids. But you can always try it. So that is why I suggest you talk to the factory they may say yes or they may say no way will it work in that service.

HMEL, I have taken your suggestion and contacted the factory,...they acknowledged receipt of my question and promised to get back with me,...I'm still waiting.

Yes, many automotive fuel pumps are now mounted "in-tank", making them a "submerged" pump, but so called "In-line" pumps are made for mounting somewhere under the car or in the engine compartment, under the hood. I purchased the In-line version which I'm sure uses fuel flow through the motor for cooling. A close examination of the motor drawing makes it appear that fuel comes in direct contact with most of the motor's internal parts, which when pumping water might lead to rust damage; another question I hope the factory will answer.

Remember, as I explained back in post #274, this fuel pump will not be the primary feed pump, it will only be used to initially ensure boiler tubes are full of water, and to provide enough steam pressure to run the second, more powerful steam turbine powered feed pump. Once the steam turbo-pump is running, the fuel-pump-feed-pump will be turned off.

 

[TimTaylor]

I plan to use a sealed system, and will start with de-ionized, highly filtered water. I don't see any way for the water to become contaminated with anything besides copper ions leached off from the boiler.
Am I missing something ??

Even in a sealed system you're probably going to have some leakage losses. The majority of potential contaminants come from the makeup water. If you're using DI water, that shouldn't be an issue, and you won't have to worry about blowdown. Na2SO3 as an oxygen scavenger is usually injected into the feedwater as a liquid. You'll probably want to buffer the pH of the boiler water with NaOH so it is on the basic side - 8.0 to 8.5. For the size of your system, it will be a very tiny amount. The actual numbers you want depend on the operating pressure. I'll dig out my Hach water treatment handbook and see if I can find some approx. numbers for you.

 

[TimTaylor]

Even in a sealed system you're probably going to have some leakage losses. The majority of potential contaminants come from the makeup water. If you're using DI water, that shouldn't be an issue, and you won't have to worry about blowdown. Na2SO3 as an oxygen scavenger is usually injected into the feedwater as a liquid. You'll probably want to buffer the pH of the boiler water with NaOH so it is on the basic side - 8.0 to 8.5. For the size of your system, it will be a very tiny amount. The actual numbers you want depend on the operating pressure. I'll dig out my Hach water treatment handbook and see if I can find some approx. numbers for you.

Did a quick look - the minimum recommended sulfite concentration in the boiler water is 20ppm. Minimum pH should never be less than 8.5, 9.0-9.5 is better.

 

[HMEL]

I plan to use a sealed system, and will start with de-ionized, highly filtered water. I don't see any way for the water to become contaminated with anything besides copper ions leached off from the boiler.
Am I missing something ??

Yes, de-ionized water has salts in it because of the way it is made. Distilled is the next quality, and ultra filtration falls some where in between. And by definition pure water is acidic although it carries a ph of seven. It has to do with the nature of a proton which is more reactive then the OH molecule. You will need water treatment and it will be very very difficult to maintain a sealed system. Especially when you get ready to design the condenser. As soon as the water turns to steam it will leave behind whatever came in with it or what ever was dissolved in it. The solids will deposit on the tube walls. A super critical boiler operates at 3206 psi and has the same operational issues you will have.

 

[NapierDeltic]

I have followed this discussion and I I'm aware of intended conditions: pure water - non-conductive, inhibitors, vapour state inside boiler ... My question : electro-chemical corrosion by using various metals in contact ( aluminum/copper ...) wouldn't raise problems ? There are both running and non-running circumstances of power plant,

 

[Toymaker]

<snip>
And by definition pure water is acidic although it carries a ph of seven. It has to do with the nature of a proton which is more reactive then the OH molecule.
<snip>

HMEL, could you please point us to the definition which you assert defines water, with a pH of 7, as being an acid.
All the Google searches I've done all define water as having neutral pH.

 

[HMEL]

I have followed this discussion and I I'm aware of intended conditions: pure water - non-conductive, inhibitors, vapour state inside boiler ... My question : electro-chemical corrosion by using various metals in contact ( aluminum/copper ...) wouldn't raise problems ? There are both running and non-running circumstances of power plant,

The wrong metals in contact such as copper fitted to steel will corrode. There exists a electro negative chart which lists the potential for this listing the metals in order. Corrosion will occur just from that electro potential and effort is generally made to avoid this in design. Liquid chemistry can be explained along some of the same theories but is generally explained in terms entropy values of the reactions that can occur. Its been awhile since I have delved into the theories. But in general you find the mistakes that were made when it is way to late to correct them. Each type of system usually has its own corrosion protection philosophy. Power plants are especially notorious for corrosion issues including stray currents from operating generators. But in general there is also the question as to the rate which is general expressed in mills material lost over time. some corrosion types occur over a long time. corrosion is one of the field of studies that is highly specialized and often one is forced to learn it rather than wanting to learn it.

 

[HMEL]

HMEL, could you please point us to the definition which you assert defines water, with a pH of 7, as being an acid.
All the Google searches I've done all define water as having neutral pH.

If you use the ph scale which defines the excess of proton ions as as acid and accept that the number of OH atoms being equal its fair to say its neutral. There are two other definitions of an acid which I would have to go look up. But the proton itself is a very hungry atom in pure water that is no other ions in solution it will react with almost anything. But it will not stay pure water for very long. Its because of the high reactivity it acts more like an acid. Water with other ions with a ph of 7 can be considered neutral.

 

[Outback]

If you use the ph scale which defines the excess of proton ions as as acid and accept that the number of OH atoms being equal its fair to say its neutral. There are two other definitions of an acid which I would have to go look up. But the proton itself is a very hungry atom in pure water that is no other ions in solution it will react with almost anything. But it will not stay pure water for very long. Its because of the high reactivity it acts more like an acid. Water with other ions with a ph of 7 can be considered neutral.

I used develop methods to analyse boiler water for power stations using ion chromatography, the requirements were low ppb (parts per billion) chloride, sulphate and other ions such as flouride bromide in other words any ion that could produce an acid eg chloride + H from water Cl will yield HCl which even though at very low concentration would impact on turbines. We also measured trace cations like sodium and calcium that will combine to form salts. A pH meter will measure the log of number of hydronium ions as mentioned 7.0 is considered neutral with a balance of H and OH ions. The power stations often add cations to boiler that will mop up trace anions like Cl that will lead to corrosion. De-ionised water is produced using a attempted balance of anion and cation ion exchange resins this often leads to slightly acid of basic output. We generally consider that water with a resistivity of less than 10 mega ohms being suitable for most high purity water applications rather that measuring pH.​

 

[Toymaker]

I used develop methods to analyse boiler water for power stations using ion chromatography, the requirements were low ppb (parts per billion) chloride, sulphate and other ions such as flouride bromide in other words any ion that could produce an acid eg chloride + H from water Cl will yield HCl which even though at very low concentration would impact on turbines. We also measured trace cations like sodium and calcium that will combine to form salts. A pH meter will measure the log of number of hydronium ions as mentioned 7.0 is considered neutral with a balance of H and OH ions. The power stations often add cations to boiler that will mop up trace anions like Cl that will lead to corrosion. De-ionised water is produced using a attempted balance of anion and cation ion exchange resins this often leads to slightly acid of basic output. We generally consider that water with a resistivity of less than 10 mega ohms being suitable for most high purity water applications rather that measuring pH.​

Did you really mean to say, "water with a resistance of GREATER than 10 mega ohms is suitable for most high purity applications" ?

 

[Toymaker]

Did a quick look - the minimum recommended sulfite concentration in the boiler water is 20ppm. Minimum pH should never be less than 8.5, 9.0-9.5 is better.

Thanks for all the help TimTaylor. I will need to purchase a small jeweler's scale (balance) to measure the less than one gram of powdered sulfite I will need for my smallish steam system .

 

[HMEL]

The ph scale is a measurement of the hydrogen ions in solution based on the dissociation constant for H2O. At exactly the value of 7.000 the number of hydrogen atoms equals the number of OH atoms. So at values above that 7.0 it contains more hydrogen atoms then OH atoms with the rest being H20. So unless the ph is exactly 7 its technically not neutral. And for every day organic things its not an issue. But it does provide protons for reactions and the water just dissociates to keep the ph at 7.0 according to its equilibrium constant.

Now there are two other definitions of acids and that is a substance being a proton or hydrogen donner (Bronstead Definition) or an electron pair donner (Lewis Definition)

Water is definitely a proton donner and its pretty evident when a tool is left out how fast it will rust. I am not sure how many people actually have reason to know about the other two definitions and in the general population a ph value is often used as the metric for an acidic or basic solution.

Not sure if I answered your question but I hope you understand why I treat water as an acid when it comes to corrosion.

 

[Outback]

Did you really mean to say, "water with a resistance of GREATER than 10 mega ohms is suitable for most high purity applications" ?

Yes 18.2 mega ohms is the highest purity 10 would be deemed accetable I would think for model boilers.

 

[TimTaylor]

Yes, de-ionized water has salts in it because of the way it is made. Distilled is the next quality, and ultra filtration falls some where in between. And by definition pure water is acidic although it carries a ph of seven. It has to do with the nature of a proton which is more reactive then the OH molecule. You will need water treatment and it will be very very difficult to maintain a sealed system. Especially when you get ready to design the condenser. As soon as the water turns to steam it will leave behind whatever came in with it or what ever was dissolved in it. The solids will deposit on the tube walls. A super critical boiler operates at 3206 psi and has the same operational issues you will have.

This information is incorrect.
1. DI water in and of itself is by definition neutral - it is neither an acid nor a base. That said, because of it's lack of ions (low ionic strength), it can be corrosive to some materials by leaching ions. It can also become very slightly acidic in some circumstances through contamination by absorption of CO2 from long term exposure to the atmosphere - not an issue in a closed system. Not an issue in any boiler system for that matter, as the pH should be adjusted somewhere in the 8.5-10.5 pH range.
2. DI water does not contain salts or other impurities. The demineralization process removes both cations and ions from the water. There is nothing in it to cause scaling, as virtually all the mineral ions that could potentially cause scaling (Ca, Mg, Fe, Cu, Na, SO4, Cl, HCO3, SiO2, etc.) have been removed. Even if there were, it would take a significant number of cycles of concentration before the ion concentration levels would approach the range where scaling could occur. In a closed system, the condensate return should be over 95%, so the amount of makeup water required will be very minimal, and if DI water is used for makeup, it will not be an issue.

It should also be noted that there are multiple grades of DI water (I, II, III), but even the lowest grade is more than sufficiently pure for most boiler water applications.

 

[peterl95124]

your free monthly reality check

1. this guy isn't building a "model" engine, its a full size engine capable of supplying enough horsepower to run a car, so the discussion shouldn't be happening here in this forum, if (maybe when) something goes wrong it could very well end up being catastrophic, you all think you're helping this guy but you might also be helping him reach that catastrophic moment.

2. All you all seem to be very mis-informed, just look at the length and volume of counter-posts to every post, its utterly insane.

3. this is a "model engine" builders forum, we swap information about the craft of machining them, but this guy is an experimenter, and he's experimenting with high powered engines, his thread isn't about machining, its about engineering, high energy, high powered, engineering, which none of you are technically qualified in, yet you're still trying to help this guy, or I should say trying to show off your knowledge in a field that you aren't actually educated in.

Whiskey-Tango-Foxtrot.

 

[minh-thanh]

your free monthly reality check

1. this guy isn't building a "model" engine, its a full size engine capable of supplying enough horsepower to run a car, so the discussion shouldn't be happening here in this forum, if (maybe when) something goes wrong it could very well end up being catastrophic, you all think you're helping this guy but you might also be helping him reach that catastrophic moment.

2. All you all seem to be very mis-informed, just look at the length and volume of counter-posts to every post, its utterly insane.

3. this is a "model engine" builders forum, we swap information about the craft of machining them, but this guy is an experimenter, and he's experimenting with high powered engines, his thread isn't about machining, its about engineering, high energy, high powered, engineering, which none of you are technically qualified in, yet you're still trying to help this guy, or I should say trying to show off your knowledge in a field that you aren't actually educated in.

Whiskey-Tango-Foxtrot.

Personal opinion
I like projects that are strange, challenging, and sometimes seem impossible, research projects...
Most of the engines I have worked on I already know how they work and I have never studied them scientifically, because the ability to understand...tools, machines... Mine is limited
Why do I like projects like that!?? What I really like is the useful and .... information... from those projects. And honestly, those projects are very informative, And I thank the members who actively contributed their ideas and comments !
About the incident...If possible, please give advice, warning...it will help if OP really listens
"model engine" builders forum: For me it doesn't necessarily mean small engines. As long as the engine is homemade it's fine. The engines I have made have a cylinder diameter smaller than 19.7mm (I usually say it is 20mm diameter because I don't care about that 0.3mm difference). So for engines with a cylinder diameter of 50mm, I have considered Is it a model engine?? Well I see it as the engine model, just the scale is different.
I have never measured the speed of the engines I have made, I think it runs fine then it is ok. If someone is trying to work on getting their engine to 50,000 rpm and that would be a very very interesting thread .
If someone needs advice ..from someone with training in model engines - an expert, a master - then there certainly won't be any opinions, comments from me, because I don't trained in small engines or an expert in it and my understanding about it is also limited
If this were a forum only about mechanics or electricity, one thing is for sure, there wouldn't be any comments from me because I have very little knowledge and experience about it.
If someone or the forum needs a trained person, a master, an expert, all my comments should be deleted.
The real important thing is : have fun, learn and share if possible !

Again, that's my personal opinion. Everything I have said on the public forum is my personal opinion

 

[HMEL]

This information is incorrect.
1. DI water in and of itself is by definition neutral - it is neither an acid nor a base. That said, because of it's lack of ions (low ionic strength), it can be corrosive to some materials by leaching ions. It can also become very slightly acidic in some circumstances through contamination by absorption of CO2 from long term exposure to the atmosphere - not an issue in a closed system. Not an issue in any boiler system for that matter, as the pH should be adjusted somewhere in the 8.5-10.5 pH range.
2. DI water does not contain salts or other impurities. The demineralization process removes both cations and ions from the water. There is nothing in it to cause scaling, as virtually all the mineral ions that could potentially cause scaling (Ca, Mg, Fe, Cu, Na, SO4, Cl, HCO3, SiO2, etc.) have been removed. Even if there were, it would take a significant number of cycles of concentration before the ion concentration levels would approach the range where scaling could occur. In a closed system, the condensate return should be over 95%, so the amount of makeup water required will be very minimal, and if DI water is used for makeup, it will not be an issue.

It should also be noted that there are multiple grades of DI water (I, II, III), but even the lowest grade is more than sufficiently pure for most boiler water applications.

Boiler water specs are rarely ever given in grades I,II,II. water specs are generally given in Ph, total disoved solids, and and other requirements. The information given is accurate for the situation we are discussing.

It depends on how the water is purified. If the cat ions are removed via a resin they are replaced with Na ions. If the salts are removed by ultrafiltration there will be ions that can not be removed by physics of ultrafiltration. One of the only ways is distillation. Water KSp constant is 10 ^-14 leaving disassociated an equal number of OH and H+ ions. H+ ions are protons which can react in solution. There is no easy way to make pure water because it is aggressive. The difference in this design is there is no drum in which a blowdown can be made. And it is the blowdown which keeps the solids in control. If you adjust the ph to below 8 it is by definition basic. If it is above 7 it is acidic. With a boiler drum the solids increase and removed with the blowdown. I dont see any way to accomplish a blowdown. Without the drum the solids will deposit on the tube walls. You will find the purest water concentration with the guys that make computer chips. Whether you use a boiler tube or a fire tube you will find a blowdown. A high pressure boiler with good quality water can expect to have a blowdown rate of 1.5 to 3% blowdown of total boiler output. The worst I have delt with is 15% in a process operation.

Over the years I have come to expect where corrosion is possible there is no such thing as neutral waters. Only specific conditions which can slow it down or speed it up.

If you are not a chemist you do not normally consider different definitions of acids and bases. The ph scale is just a measure of the available hydrogen ions in solution. The more of them the faster the rate of reaction. There is also an pOH scale that is sometimes used for some reactions.

But to change the ph you need to add an acid or base in water to form a buffer solution. These are salts and they will deposit somewhere. And we have not even touched the subject of entrained gases.

But there is an old saying the proof is in the pudding. Build it, put water in it and see what happens.

 

[Toymaker]

<snip> If you adjust the ph to below 8 it is by definition basic. If it is above 7 it is acidic.

I'm sure you really meant to say the opposite; that pH values below 7 are acid and above 7 are bases.

With a boiler drum the solids increase and removed with the blowdown. I don't see any way to accomplish a blowdown.
<snip>

Stanley Steam cars would simply open a valve and vent the boiler water every few hundred miles,...no reason I cannot do the same with my boiler. Then refill with a few gallons of distilled water. Cheap and easy.

<snip>
But there is an old saying the proof is in the pudding. Build it, put water in it and see what happens.

 

[ajoeiam]

snip

If you adjust the ph to below 8 it is by definition basic. If it is above 7 it is acidic.
snip

Are you sure about these two statements?