I will explain the nozzle orientation of the tank .
Nozzle orientation is a fairly complex part of tank design.
The limit is to decide the capacity of the tank and decide the plate thickness .
There are so many patterns.
As a result, when we received the drawings from the manufacturer, we were troubled and decided to make the same layout as the existing facility or only consider the connection of the pipes.
But this is not good enough.
I would like to take the form of determining the main constraints on the orientation of the nozzle from the standpoint of mechanical design, and then factoring in the convenience of equipment manufacturing and piping layout.
Nozzles can be designed by prioritizing them!
Design Elements Affected by Tank Nozzles
I summarized the design elements that are affected when the nozzle of the tank is a design variable.
Let’s understand the basics when considering nozzle orientation.
Workability
The biggest factor affected by nozzles is workability .
- On-site driving work
- construction work
Think in two ways.
Among recent mechanical and electrical engineers, there is a tendency to prioritize over on-site work.
If you’re an owner-engineer, you want to give priority to on-site work .
cost
Nozzles affect cost .
The more nozzles, the higher the cost.
Obvious but important.
- Will adding one nozzle fit within the budget of the project?
- Does the added nozzle perform the function commensurate with the amount of money?
I have to think about this.
I don’t know the function, but it would be fine if there was an intention to add it for the time being, but the reality is that I don’t even want to add a nozzle.
As expected, I want you to see the budget, but there are many engineers who ignore it because the amount is small .
room for expansion
The number of nozzles affects future expansion room .
This is also a matter of course.
However, the idea of plant design comes out quite strongly here.
Strength
The number of nozzles affects the strength of the equipment .
The greater the number of nozzles, the lower the strength.
It is a matter of course, but (omitted below)
The owner engineer usually leaves the calculation of the strength of the tank to the manufacturer, so I think that the manufacturer will do something about adding one nozzle .
I would like to think about whether it is necessary to add nozzles even if the strength is reduced.
Batch-type chemical plants are used only under fairly low pressure conditions, so this is of little concern, but I would like to understand it accurately in the sense that it does have an effect .
If there is a bottoming nozzle
From here, we will consider the nozzle orientation of the tank.
Consider the case where the tank has a bottoming nozzle .
Features of bottoming nozzle
Let’s first organize the features of the bottomless nozzle.
It may seem obvious, but by verbalizing it, you can see the essence.
All liquid can be drained
If there is a bottom extraction nozzle, the entire amount of liquid can be removed.
Conversely, it is not possible to drain the entire amount of liquid without a bottom drain nozzle.
It seems obvious, but it is very important.
This is especially important in batch systems.
Switching production means that process equipment must be cleaned.
If you try to wash it to the extent that it can be used with the next product,
Full drain works very well.
Even in a continuous factory, it is necessary to drain the entire amount of liquid, although there is a difference in degree.
Therefore, a considerable amount of equipment in chemical plants consists of equipment with bottomless nozzles.
Drainage in the center of the bottom
When bottoming out, it is basic to pull out toward the center.
This seems obvious, but it’s also important.
This is to ensure that the weight balance of the equipment is centered.
It will look like the image below.
Leakage is a big deal
It can be said that attaching a bottomless nozzle allows the entire amount to leak once it leaks .
Of course.
It is a bottomless nozzle that assumes full extraction, and if by any chance leaks from the nozzle, the entire amount will leak.
It doesn’t matter if it’s a safe liquid such as water, and it doesn’t matter if it’s around the water in your house.
However, it should be borne in mind that for tanks with hazardous chemicals, bottoming nozzles have both advantages and disadvantages.
So many machines have bottomless nozzles that some people take it for granted, but I want to warn you.
There are cases where the bottom-out nozzle line of the tank has a threaded joint or a sandwiched part , but this is a design that does not consider the risk of leakage .
top of tank
Orientation of tanks with bottoming nozzles is limited to tank top issues.
This is understandable given the installation situation.
The installation image of a tank with a bottom extraction nozzle is as follows.
There is a human access area on top of the tank where there is some work.
Since it has a bottoming nozzle, the tank must be lifted off the floor .
Set the height of the bottoming nozzle itself to a place where a person can work.
Then the top of the tank will be in a very high position.
Accessing and working here becomes a big problem.
Some tanks may have functions such as horizontal extraction and horizontal extraction, but this is a rare case, so I will exclude it this time.
Nozzle orientation on top of tank
Look at the nozzle orientation on the top of the tank.
It will look like the image below.
central gas line
Place the gas line in the center of the tank .
This is an image of a case where the upper part of the tank is a dish type or a cone roof type.
There is no necessity to place it in the center of the tank with a flat lid tank,
In the sense of unifying the design concept, I think it is easier to understand if it is placed in the center.
When installing a stirrer in the center of a tank such as a reactor, the gas line cannot be placed in the center, but let’s consider that separately.
The manhole is located near the passage
Place the manhole near the passage .
Of course this is also natural.
I would like to install a handhole of about 200A even in a small tank where there is no room for a manhole.
In any case, the location of the large nozzle, the manhole, should be determined first.
In batch chemical plants the exception would be limited to powder systems.
Header on work area side
Place the header on the work area side .
The work area is the part near the manhole.
It’s a header, so it’s a mouth that receives liquid.
Since the liquid receiving header is usually equipped with a valve, place it on the work area side to operate the valve.
In some cases, only the nitrogen inlet is a single nozzle, but it is better to place this on the work area side as well.
Avoid nozzles in non-working areas
Place nozzles for other purposes in non-working areas.
The non-work area is located on the opposite side of the manhole.
I don’t want to place the nozzle itself in the non-working area.
Even if it is attached, I would like to limit it to the following uses.
- lighting port
- Liquid level indicator
- rupture disc
These are applications that require less work and less frequent inspections.
When there is no bottoming nozzle
I will explain the case of a tank without a bottom extraction nozzle .
This is an image of a flat-bottomed tank , such as an outdoor tank .
What is the reason for the flat bottom shape of the tank storage tank?
It’s too basic to be asked again, isn’t it?
There are several reasons for choosing a flat-bottomed tank, but the most common ones are:
- very large tank capacity
- reduce costs
- Full liquid transfer is not required
Outdoor tanks are basically flat-bottomed because of their large capacity.
The larger the shape of the tank, the higher the degree of freedom in nozzle orientation and the more difficult it becomes.
In designs with high degrees of freedom, the first consideration should be to limit the degrees of freedom.
Keep a distance between the side plate manhole and the top plate manhole
The first nozzle to be designed in nozzle orientation is the manhole .
Not limited to nozzle orientation, it is important to “decide in order from the largest” in plant design.
It is the same as deciding the reactor and tower first in plant construction .
The manhole is the largest of the nozzles.
Let’s decide from here.
The basic idea of the manhole is to ” take a distance between the top plate manhole and the side plate manhole “.
The image is as below.
A manhole is attached to the side plate of a flat-bottomed tank that cannot be completely drained.
This is for people to come in and clean up.
Not only side manholes but also top manholes are required. this is,
It comes from the idea that when replacing the inside of the system with air, the amount of stagnation can be reduced .
The position of the manhole is almost determined by this alone.
Manhole restrictions
Separate the top plate manhole and the side plate manhole as much as possible
Manhole location is a major constraint on nozzle orientation.
Separate the liquid inlet nozzle from the liquid outlet nozzle
Next to the manhole, consider the positional relationship between the liquid inlet nozzle and the liquid outlet nozzle .
There are constraints here as well.
There is a problem if the inlet nozzle is too close to the outlet nozzle.
When the liquid enters the tank, the gas dissolved in the liquid goes out to the gas phase.
If this is close to the liquid discharge nozzle, air bubbles will be caught in the pump side, and cavitation will easily occur.
Constraints on liquid inlet/liquid outlet nozzles
Keep the liquid inlet nozzle and the liquid outlet nozzle as far apart as possible.
This is a constraint condition for the liquid inlet and liquid outlet nozzles.
Restrictions on the manhole side and restrictions on the nozzle side work as a set.
Location of tank and pump
It turned out that the tank alone has restrictions on manholes and nozzles.
In order to determine the nozzle orientation of a tank, it must be related to other elements, not just the tank itself.
A typical example is a pump .
The distance between the tank and the pump should be as close as possible .
It is natural for the purpose of cavitation prevention and minimization of pipe length .
However, when trying to determine the position of the pump , there are unexpected restrictions.
- Is the pump close to the passage?
- Is there a piping rack near the pump?
- Can you pull the lorry closer to the pump?
Since the position of the pump is directly linked to workability, it is a major constraint.
Constraints on liquid inlet/liquid outlet nozzles
As close as possible to the liquid outlet nozzle from the pump position
Minimize the work on the top board
For flat-bottomed tanks and other tanks that do not have bottom extraction nozzles, it is desirable to minimize work on the top plate .
The presence or absence of work on the top plate is determined by the relationship between the tank nozzle and piping parts.
- It is preferable that the net and the opening of the flashback prevention device are on the top plate.
- Piping valves and check valves are preferably above ground.
- It is preferable to install the pipe block plate on the ground.
- When connecting multiple pipes to a tank, it is preferable to assemble the headers on the ground as much as possible.
- The nozzles on the top plate are not uniform in all directions, and it is better to set them in one direction .
The fewer pipes and accessories that must be installed on the tabletop, the better.
The work of regularly climbing high tabletops should not be generalized.
The idea of fixing it to one side of the nozzle on the top plate would never occur to an ordinary plumbing engineer.
This is a point that mechanical engineers should be aware of.
The image is as follows.
Set up a work area on the top plate near the manhole.
It is preferable to place the liquid filled nozzle close to this working area.
It is better not to install nozzles as much as possible in places away from manholes on the top plate.
This is because the size of the working deck becomes excessively large.
Even if the size of the tank is large, the actual area required for work is not large, and it is cost effective to concentrate the work area.
Provide space for the piping to rise outside the work area and manholes .
This is not a big restriction for the tank, but it would be better to remove it from the top plate and side plate manhole.
The space for rising the piping is determined by the position of the surrounding piping racks, so it is determined by the positional relationship between the tank and the pump .
It is the liquid drain nozzle that affects the positional relationship between the tank and the pump .
Accessories (gate/liquid level gauge)
As you stack the constraints above, the degree of freedom for nozzle orientation drops considerably.
Specifically, it can be limited to:
- Determine the position of the manhole on the top plate and side plate,
- Once the orientation of the liquid inlet and liquid outlet is determined,
- Determines the rise position of the piping.
- Place the entrance in a position that avoids the rising position of the piping.
- Place the liquid level gauge between the liquid inlet and liquid outlet.
Once this is decided, the rest is limited to detailed position settings.
The No. 5 liquid level gauge is placed “between the liquid inlet and the liquid drain port” because it is assumed to be a differential pressure type liquid level gauge.
If a differential pressure type level gauge is installed near the liquid inlet or liquid outlet, it will be susceptible to liquid pulsation.
The part where the dynamic pressure due to the movement of the liquid is the lowest is the part between the liquid inlet and the liquid drain port.
If the nozzle position of the liquid inlet and liquid outlet is secured at 180 degrees, it is good to bring the differential pressure type liquid level gauge to the position of 90 degrees.
This is the orientation with the maximum flow area .
In addition, since it is necessary to provide the pressure equalization port of the differential pressure type liquid level gauge on the top plate, the nozzle must be set up on the top plate.
Since we also want to minimize the pressure equalization line, we set up the nozzle on the top plate in the same direction as the mounting direction of the level gauge.
Then you have to set up the entrance in a slightly shifted place.
If the tank size is large, it will not be a problem, but if it is halfway small, it tends to be a little difficult to find the entrance.
Since it is not possible to completely satisfy all the constraints, we have to compromise to some extent, and the hatches and liquid level gauges are easy targets.
Standardization and specialization
The nozzle orientation of the tank is considered in two patterns: standardization and specialization .
The examples considered above are all examples of specialization .
It is designed from the viewpoint of determining the optimum nozzle orientation for a specific tank .
This is less of a problem with iron or stainless steel tanks .
This is because there is very little room for future expansion.
However, this is not the case with glass lined or fluorine resin lined tanks .
In the case of batch production assuming changeover production, a larger number of nozzles can reduce changeover work .
You will have to think about how many nozzles will make work easier, but if you think about that, it is better to add as many nozzles as possible within the range where strength is not a problem .
This is the idea of standardization .
If you are aiming for a standard nozzle, consider the following factors.
standard nozzle
- Manhole is 400A and 450A
- Gas line/powder inlet is 200A
- Dedicated baffle
- All other lines are 100A
This assumes a tank of 10m3 or more.
If it is a smaller tank, the caliber may be smaller.
This is because the smaller the capacity of the tank, the smaller the nozzle size that can be installed , and the smaller the flow rate of the liquid transfer pump, the smaller the pipe diameter .
If you do not secure a nozzle for the gas line and powder inlet for the standard tank, it will easily affect the situation later.
If you attach a flange to the main unit so that the top plate can be replaced, it is possible to modify it later, but it is better not to do so because it will leak easily and increase the wasted space capacity.
In that case, once the tank is installed, it cannot be replaced later, so it is important to think about it first.
reference
There are few textbooks on tank design.
Rather, it is related to plant design and piping design.
That is why it is necessary to understand the concept of plant design and piping design before equipment design.
lastly
I introduced the concept of the nozzle orientation of the tank.
Nozzle orientation affects workability, cost, room for expansion, strength, etc.
We will introduce the concept of dedicated nozzle orientation, divided by the presence or absence of bottomless nozzles.
It also introduces standardization.
Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (The comment section is at the bottom of this article.)
*I will read all the comments and answer them seriously.