Please, expert, regarding the issue of boiler paralleling!
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This post was last edited by Clgg0822 on 2021-10-11 at 10:10. There are two gas-fired hot water boilers, with an evaporation capacity of 6 tons each; the allowable operating pressure is 1.25 MPA, and they operate in parallel. The steam used at the end user side has a pressure of 0.7 MPA. During actual operation, the maximum instantaneous flow rate reaches only 8 tons, and whenever the load at the end user side increases, the pressure of the boilers drops sharply. I’m asking for advice from experts: Is this operating condition normal? It would be great if you could explain the situation regarding the boiler. Thank you!
One more thing: the actual set pressure of the boiler is 0.8 MPa
This question isn’t quite clear. 1. A gas hot water boiler is supposed to produce hot water. Later you mentioned evaporation rate; this refers to steam boilers. That’s inconsistent, right? 2. Is the model for a single unit WNS6-1.25-Q or WNS3-1.25-Q? It’s not clear from the question whether the 6 tons refers to the total amount or the evaporation capacity per unit. 3.8 tons refers to the usage amount of steam equipment, right? First, clarify the issue so we can discuss it together. Under normal circumstances, if the boiler’s steam production is 12 tons (6 tons per unit) and the steam consumption remains within 12 tons, there is no need to release pressure. Is there a system diagram? Everyone, take a look. For example, whether the layout of the cylinder banks is reasonable or not.
Sorry, I made a mistake earlier; it’s a steam boiler, with the model number WNS6-1.25-Q for each unit. There is no layout diagram for the steam distribution cylinders; the actual operating conditions are as follows: the set pressure of the boilers is 0.8 MPa, and the total instantaneous flow rate through each steam pipe coming from the steam distribution cylinders is around 8 tons. Once the load at the user end increases, the operating pressure of both boilers drops sharply
If the total flow rate of the meter is 8 tons, it means that the two boilers were originally designed as WNS6-1.25-Q, but are actually being used in mode WNS4-0.8-Q, with reduced rated pressure and reduced steam output. Assuming the user’s total consumption is 9 t/h, the steam supply from the boiler will be insufficient; it’s like using a weak horse to pull a heavy load, which can be likened to a water pump that isn’t able to deliver enough flow. There is negative pressure inside the boiler drum compared to normal operation, and it’s normal for the pressure gauge to show a decrease. This boiler should be of three-pass type; the impact is not significant. It can be tried with the model WNS4.5-1.0-Q (assuming a usage rate of 9 t/h). In any case, it’s necessary to first determine the user’s usage rate in order to adjust the steam output of the boiler accordingly. It’s just my personal opinion; it’s not necessarily correct. I’m just trying to provide some input to stimulate further discussion among the experts.
Can the work pressure be set, and can the evaporation rate also be set? If the evaporation rate cannot be set manually on-site, I think the total output can exceed 12 T of steam. Is my understanding correct?
Another question is: for the WNS6-1.25-Q boiler, if the actual operating pressure is set at 0.8 MPa, will the output volume of gas decrease? Or can I maintain an output volume of 12 tons regardless of the pressure setting?
You can think of this rated evaporation rate as the speedometer in our car – how is it possible for 220 to turn into 300, right? There is a maximum limit for this. But you can run 30, or just 1 – it’s fine either way. For example, in the case of a 6-ton boiler, the upper limit is 6 tons. You can also produce at 1 ton, but the efficiency is too low, resulting in waste fuel. I have explained it in the simplest terms possible; I’m not sure if it was clear enough.
Pressure corresponds to steam temperature: 1.25 represents saturated steam at over 190°C, while 0.8 corresponds to a saturated steam temperature of around 180°C. The exact values can be found in tables. This temperature is related to the steam supply temperature agreed upon between the user and you; it represents the requirements of their manufacturing process. The steam output can reach 12 t/h; it may also be lower than that, but it will not exceed 12. This relates to the arrangement of the heating surfaces inside the boiler; you can take a look at the thermal calculations in the accompanying materials.