Gas boilers use natural gas and LPG as fuel – how to consider making a switch?

Firstly, there is a significant difference between the calorific value and molecular weight of natural gas and liquefied gas. In principle, the burner of your gas boiler is designed for one type of fuel gas; therefore, it is necessary to pay attention to the opening degree of the gas control valve during actual use； Secondly, it is likely that the poster also switched to using liquefied gas as a fuel due to the skyrocketing prices of natural gas. Liquefied gas is in a liquid state at certain pressures, which hinders complete combustion; in severe cases, this can even lead to safety accidents. It is recommended that a vaporizer be added to the system for handling liquefied gas ； Third, this mixing method follows a principle-based process, and relevant flow rates, pressures, pressure reduction devices, safety valves, etc. all need to be installed

There’s nothing wrong with the process; this is the most basic process available. But there aren’t any monitoring points at all – at least there should be pressure gauges at both ends! Otherwise, when you switch, the high-pressure medium will mix into the low-pressure medium! Switching principle: 1. When switching from a high-pressure medium to a low-pressure medium, it is necessary to reduce the pressure of the high-pressure medium using valves or other means to a level slightly higher than that of the low-pressure medium, while ensuring normal combustion in the furnace. Thereafter, the valve for the low-pressure medium should be slowly opened to carry out the switching process, until the valve for the high-pressure medium is fully closed; the valve for the low-pressure medium should then be adjusted as needed to meet the production requirements! ! 2. Conversely, when using a low-pressure medium to cut through a high-pressure medium, slowly open the valve for the high-pressure medium; ensure that its pressure is slightly higher than that of the low-pressure medium, then gradually close the valve for the low-pressure medium until it is fully shut off. After that, adjust the valve for the high-pressure medium as needed to meet the production requirements!

This post was last edited by arpcd on 2017-12-28 at 14:20. I would like to ask the original poster: LPG burners are different from natural gas burners; just look at household stoves to see this. A stove designed for LPG won’t work well with natural gas. Switching between fuels isn’t that difficult, so surely your burner isn’t the same type for both fuels? Since both are measured in terms of volume (Nm3), there is a huge difference in their calorific values: natural gas has a calorific value of 8,000–9,000 kcal/m3, while LPG has a value of around 24,000–26,000 kcal/m3. The reason why the same burner cannot be used is that such a large difference in calorific values leads to a significant difference in the amount of air required (per 1 Nm3 of fuel gas). Recommendation: Install an air pipeline alongside the LPG pipeline, and strictly control the ratio of LPG to air. The resulting mixed gas should have parameters such as calorific value comparable to those of natural gas, so that there is no need to change the burner.

Thank you for your advice! May I ask, is it effective to install check valves separately on natural gas and LPG?

Thank you for your advice! The burner air inlet is now equipped with a blower that can adjust its frequency. Can the air volume at the fan be adjusted to control the LPG-to-air ratio?

From a technical standpoint, check valves are fine as they can prevent the backflow of fluid; however, their practical usefulness is limited. The valve discs in check valves usually allow some internal leakage. To enable switching between two streams, several additional valves can be used, and such switches should be placed as close as possible to the combustion nozzle of the heater. Additionally, the pressures of the two fuel gases need to be taken into consideration – if the pressure is too high, pressure regulators or self-acting control valves are required, and these should be installed for both streams: for pressure, flow rate, rapid shutdown, venting, and condensate drainage