Hi everyone,
I apologizes in advance because this post will be too long.. Really sorry for that.
I have some problems in the design of a Sodium Metabisulfite plant for a gold mine.
I'll explain all the content and basically is as follow:
ENVIROMENTAL CONDITIONS
Humidity is around 70-90%
Temperature range: 1°C - 15°c
Altitude: 4000 m.a.l.s
For this project we though in two alternative
[highlight #FCE94F]FIRST ALTERNATIVE (The client will not consider a continuous process system)
[/highlight]
The Silo was thought just for stockage and the system automatically will feed this product to the process.
Disadvantages of using a silo?
Transport chemical into the silo using a screw conveyor.
We are thinking that due to the hygroscopic properties of the powder, use a screw conveyor that long to transport the powder to the silo would not be a good idea since that moisture can affect (in some way) the conveying, forming cakes (agglomeration) inside of it. At the end the screw might be affected by this fact and finally stop functioning.
This is a comment from screw feeder manufacturer:
So, since this product is quite hygroscopic, the problem mentioned above easily can happen. And for avoiding this we will need to use some kind of moisture extractor. Therefore, I think is not convenient use a screw conveyor for this case.
The client itself says there are always problem when we’re talking about using screws.
Additionally, this powder can get in contact with air, especially humidity air, so a dehumification system will be required. This could increase the cost of the project and the operating cost (maybe).
What do you think about this consideration?
Do you really think moisture can affect the screw functionality?
Would it be necessary use a dehumification system in this case?
What do you recommend for handling Sodium Metabisulfite?
Currently, customer says just consider use a batch system.
The chemical supplier also recommend not storage this powder for a considerable time at the actually environment conditions. They say that will be preferably prepare a great amount of solution because aqueous solution is more stable than raw chemical (powder).
So based on this we are thinking not consider use screws.
So this is the second alternative:
[highlight #FCE94F]SECOND ALTERNATIVE: BATCH SYSTEM
[/highlight]
This is what we are thinking.
Lift up the bulk bag several meters up, move it horizontally with a monorail and put the bulk bag on the bulk bag discharger that will be at the top of the thank and use a rotary valve to dosing this powder into a make-up tank (preparation tank + agitator).
After that use an enough amount of this powder to prepare a solution and maintain storage of this solution (Sodium MBS + Water at 30%) for around 7 to 12 hours. Pumping this solution into the storage tank and repeat the process until make enough of this solution to fill the tank. The storage tank has to be suitable to retain 12 hours of the solution.
Problems to take into consideration:
BULK BAG DISCHARGER
- The bulk bag discharger probably will need a dust collector too.
- I’m afraid of moisture can affect in some way after breaking the bag, the powder will fall into a kind of hopper of low capacity (300 kg maybe) (Look at the pictures below for reference)
- For example, when the content of the bag has finished discharging, you remove this bag….just in that moment the air and moisture can get into the cylinder, and when you break a new bulk bag, the powder will get in contact with the previous moisture I’m talking about. Maybe this can be considered a trivial matter and there would have no problem at all. But I have several doubts about this.
- Additionally, do you think a dust collector for the bulk bag discharger would be required? Maybe we will need to enclose all the bulk bag in a metallic cabin.
- Once this powder get in contact with air loss part of its SO2 available (starts to oxidize). This is not convenient, the manufacturer says that is storable just when kept dry and protected from air.
- So the last comment makes me think that we can use Silo (because of the consumption – 19 ton per day) as long as we protect this powder from air and moisture. But that would lead to use screw conveyor to transport the powder to the SILO and WE DON’T WANT THAT unless someone can really give me a guarantee that with this way there would have no problem. It would be great if you can show me an actual system working on this way (but obviously using Sodium MBS)
MAKE UP TANK
- This tank is for preparing a solution of Sodium Metabisulfite + water at 30% of concentration.
- This tank is closed to the atmosphere
- When you mix water and Sodium MBS you obtain just Sodium Bisulfite (BS) according to the following reaction:
Na2S2O5 + H2O + 2NaHSO3.
In that expression it not appears but after reading about what happen when Sodium MBS is mixed with water this solution release SO2, the releasing of SO2 depends basically on the temperature and the Ph of the solution and maybe the % of the solution concentration.
The problem is that I don’t know how much of this gas will be given off and this is a matter of concern.
I’m thinking that I will need to use a scrubber, but honestly don’t know if this will be a solution.
This is the recommendation of the chemical supplier.
- They recommend to use dry air in case of a low dissolution temperature (that’s the case) and N2 for higher dissolution temperature (above 30°C) to prevent oxidation.
The waste air contain SO2 and has to be washed out by water or more effectively with a sodium hydroxide solution.
So this makes me think a scrubber can’t be avoided, but I don’t know that much about this, so I don’t know what parameters are required for selecting a proper scrubber.
Is there a way to determine how much SO2 will be release at the operation conditions (minimum temperature of 1°C and 30% of solution concentration)?
The supplier also says that the solution must be stored in O2-free atmosphere or otherwise the bisulfite solution becomes oxidized (to sodium sulfate. But, how can I eliminate the Oxygen in the tank? I think air (with Oxygen) always can get into the tank, because of this:
- Water inlet
- Ingress of the powder (maybe)
- Another factors that I don’t’ know
I don’t really know how to avoid contact with O2, but maybe can’t be avoided and the amount oxidized product is negligible if we compare it with the rest of the product.
- What would you recommend in this case?
- The chemical supplier says also that at the current environment conditions we can use dry air to prevent oxidation N2 is just for temperatures higher than 30°C (contradictory use dry air? – dry air also contains O2?)… But how much air would I need to inject to the solution? Continuous? Just a few amount? How can I determined this?
STORAGE TANK
The solution must be used as soon as possible because of a restricted shelf life (oxidation to sodium sulphate). To prevent oxidation during longer time of storage, use nitrogen as a layer above the surface of the solution.
This tank is closed to the atmosphere as well.
The client want a storage tank for 7 hours of independence/autonomy.
This is not strictly necessary, we are considering a tank for at least 12 hours.
The process must work for 24 hours/7 days
The problems for the storage tank are as follow:
- How to eliminate O2 from this tank?
- Again, the costumer says that aqueous solution also can release SO2 and therefore, would it need a scrubber too?
- If that the case, can I interconnect both of these tanks (make up and storage) with just one scrubber?
- The supplier say that this solution must be used quickly to avoid oxidation to sodium sulphate. To avoid oxidation for longer time of storage, we will need to use N2 as a layer above the surface of the solution. However, they also say they 1 day of storage is not critic.
- The main problem is the releasing of SO2 and the way of treat this gas.
- This would be the basic scheme:
- What would be the best way to transport the given off gases? With what tool or equipment?
- And the same than make up tank:
Maybe I will need to inject dry air into the tank, but how much air would I need to inject to the solution? Continuous? Just a few amount? How can I determined this?
VAPOR SEAL TANK
Just look at the following picture:
This is the same process but much better drawn.
As you can see the spaces remarked in red are apparently where the given off gases will be transferred.
To obtain a better view of the drawing look at the following figure:
It appears to be that client is already aware about the releasing gases and that’s why they put in their diagram one tank for vapor seals. I can suppose they are going to treat this with a chemical or something.
But the doubts are the same.
- What would be the best way to transport the produced gases to this tank?
I don’t know that much about this so I can only think about a scrubber, but maybe there is another way.
- Can you give me a suggestion about how to transport this gases to that tank?
I think this would be all my doubt about this. I know is too much information but with this you can give me some suggestions about this and cleared me up all this doubt I have.
Thanks in advance and sorry again for this too long post.
Regards,
I apologizes in advance because this post will be too long.. Really sorry for that.
I have some problems in the design of a Sodium Metabisulfite plant for a gold mine.
I'll explain all the content and basically is as follow:
ENVIROMENTAL CONDITIONS
Humidity is around 70-90%
Temperature range: 1°C - 15°c
Altitude: 4000 m.a.l.s
For this project we though in two alternative
[highlight #FCE94F]FIRST ALTERNATIVE (The client will not consider a continuous process system)
[/highlight]
The Silo was thought just for stockage and the system automatically will feed this product to the process.
Disadvantages of using a silo?
Transport chemical into the silo using a screw conveyor.
We are thinking that due to the hygroscopic properties of the powder, use a screw conveyor that long to transport the powder to the silo would not be a good idea since that moisture can affect (in some way) the conveying, forming cakes (agglomeration) inside of it. At the end the screw might be affected by this fact and finally stop functioning.
This is a comment from screw feeder manufacturer:
So, since this product is quite hygroscopic, the problem mentioned above easily can happen. And for avoiding this we will need to use some kind of moisture extractor. Therefore, I think is not convenient use a screw conveyor for this case.
The client itself says there are always problem when we’re talking about using screws.
Additionally, this powder can get in contact with air, especially humidity air, so a dehumification system will be required. This could increase the cost of the project and the operating cost (maybe).
What do you think about this consideration?
Do you really think moisture can affect the screw functionality?
Would it be necessary use a dehumification system in this case?
What do you recommend for handling Sodium Metabisulfite?
Currently, customer says just consider use a batch system.
The chemical supplier also recommend not storage this powder for a considerable time at the actually environment conditions. They say that will be preferably prepare a great amount of solution because aqueous solution is more stable than raw chemical (powder).
So based on this we are thinking not consider use screws.
So this is the second alternative:
[highlight #FCE94F]SECOND ALTERNATIVE: BATCH SYSTEM
[/highlight]
This is what we are thinking.
Lift up the bulk bag several meters up, move it horizontally with a monorail and put the bulk bag on the bulk bag discharger that will be at the top of the thank and use a rotary valve to dosing this powder into a make-up tank (preparation tank + agitator).
After that use an enough amount of this powder to prepare a solution and maintain storage of this solution (Sodium MBS + Water at 30%) for around 7 to 12 hours. Pumping this solution into the storage tank and repeat the process until make enough of this solution to fill the tank. The storage tank has to be suitable to retain 12 hours of the solution.
Problems to take into consideration:
BULK BAG DISCHARGER
- The bulk bag discharger probably will need a dust collector too.
- I’m afraid of moisture can affect in some way after breaking the bag, the powder will fall into a kind of hopper of low capacity (300 kg maybe) (Look at the pictures below for reference)
- For example, when the content of the bag has finished discharging, you remove this bag….just in that moment the air and moisture can get into the cylinder, and when you break a new bulk bag, the powder will get in contact with the previous moisture I’m talking about. Maybe this can be considered a trivial matter and there would have no problem at all. But I have several doubts about this.
- Additionally, do you think a dust collector for the bulk bag discharger would be required? Maybe we will need to enclose all the bulk bag in a metallic cabin.
- Once this powder get in contact with air loss part of its SO2 available (starts to oxidize). This is not convenient, the manufacturer says that is storable just when kept dry and protected from air.
- So the last comment makes me think that we can use Silo (because of the consumption – 19 ton per day) as long as we protect this powder from air and moisture. But that would lead to use screw conveyor to transport the powder to the SILO and WE DON’T WANT THAT unless someone can really give me a guarantee that with this way there would have no problem. It would be great if you can show me an actual system working on this way (but obviously using Sodium MBS)
MAKE UP TANK
- This tank is for preparing a solution of Sodium Metabisulfite + water at 30% of concentration.
- This tank is closed to the atmosphere
- When you mix water and Sodium MBS you obtain just Sodium Bisulfite (BS) according to the following reaction:
Na2S2O5 + H2O + 2NaHSO3.
In that expression it not appears but after reading about what happen when Sodium MBS is mixed with water this solution release SO2, the releasing of SO2 depends basically on the temperature and the Ph of the solution and maybe the % of the solution concentration.
The problem is that I don’t know how much of this gas will be given off and this is a matter of concern.
I’m thinking that I will need to use a scrubber, but honestly don’t know if this will be a solution.
This is the recommendation of the chemical supplier.
- They recommend to use dry air in case of a low dissolution temperature (that’s the case) and N2 for higher dissolution temperature (above 30°C) to prevent oxidation.
The waste air contain SO2 and has to be washed out by water or more effectively with a sodium hydroxide solution.
So this makes me think a scrubber can’t be avoided, but I don’t know that much about this, so I don’t know what parameters are required for selecting a proper scrubber.
Is there a way to determine how much SO2 will be release at the operation conditions (minimum temperature of 1°C and 30% of solution concentration)?
The supplier also says that the solution must be stored in O2-free atmosphere or otherwise the bisulfite solution becomes oxidized (to sodium sulfate. But, how can I eliminate the Oxygen in the tank? I think air (with Oxygen) always can get into the tank, because of this:
- Water inlet
- Ingress of the powder (maybe)
- Another factors that I don’t’ know
I don’t really know how to avoid contact with O2, but maybe can’t be avoided and the amount oxidized product is negligible if we compare it with the rest of the product.
- What would you recommend in this case?
- The chemical supplier says also that at the current environment conditions we can use dry air to prevent oxidation N2 is just for temperatures higher than 30°C (contradictory use dry air? – dry air also contains O2?)… But how much air would I need to inject to the solution? Continuous? Just a few amount? How can I determined this?
STORAGE TANK
The solution must be used as soon as possible because of a restricted shelf life (oxidation to sodium sulphate). To prevent oxidation during longer time of storage, use nitrogen as a layer above the surface of the solution.
This tank is closed to the atmosphere as well.
The client want a storage tank for 7 hours of independence/autonomy.
This is not strictly necessary, we are considering a tank for at least 12 hours.
The process must work for 24 hours/7 days
The problems for the storage tank are as follow:
- How to eliminate O2 from this tank?
- Again, the costumer says that aqueous solution also can release SO2 and therefore, would it need a scrubber too?
- If that the case, can I interconnect both of these tanks (make up and storage) with just one scrubber?
- The supplier say that this solution must be used quickly to avoid oxidation to sodium sulphate. To avoid oxidation for longer time of storage, we will need to use N2 as a layer above the surface of the solution. However, they also say they 1 day of storage is not critic.
- The main problem is the releasing of SO2 and the way of treat this gas.
- This would be the basic scheme:
- What would be the best way to transport the given off gases? With what tool or equipment?
- And the same than make up tank:
Maybe I will need to inject dry air into the tank, but how much air would I need to inject to the solution? Continuous? Just a few amount? How can I determined this?
VAPOR SEAL TANK
Just look at the following picture:
This is the same process but much better drawn.
As you can see the spaces remarked in red are apparently where the given off gases will be transferred.
To obtain a better view of the drawing look at the following figure:
It appears to be that client is already aware about the releasing gases and that’s why they put in their diagram one tank for vapor seals. I can suppose they are going to treat this with a chemical or something.
But the doubts are the same.
- What would be the best way to transport the produced gases to this tank?
I don’t know that much about this so I can only think about a scrubber, but maybe there is another way.
- Can you give me a suggestion about how to transport this gases to that tank?
I think this would be all my doubt about this. I know is too much information but with this you can give me some suggestions about this and cleared me up all this doubt I have.
Thanks in advance and sorry again for this too long post.
Regards,
![[dazed]](/data/assets/smilies/dazed.gif "[dazed] [dazed]")
