I have a boiler operating at 5bar and produces saturated steam. From steam tables, the temperature is 151.9 degrees Celcius. I have tried using the continuity equation but the answer is not right. I need another mathematical option apart from using a guage to measure.
I know this sounds like an undergraduate question but oh....i cant get my finger around it. Could someone please help me? Thank you
Do you know the inlet temperature and amount of fuel used? If yes, use the energy balance equation to determine the steam mass flow rate.
The information you give is not enough to answer the question. The basic relationship is:
Q = m ΔH
where m is flow rate (kg/s), Q is the rate of heat transfer (kJ/s), and ΔH is the enthalpy change between inlet and outlet. With the information you give you can only calculate the enthalpy at the exit of the boiler.
You gave insufficient amount of data. The temperaturę and pressure can be as well obtained at closed main steam valve (no flow conditio) as at the full flow. The flow is determinated mainly by the consumption.
More data are needed, for example volume flow or energy supply and inlet fluid temperature.
Thank you all.
The boiler uses 147l/hr of fuel, the water inlet temperature is 25degrees Celsius and its maximum steam output is 2tonnes/hr. my aim is to determine the steam flow rate at a lower pressure than the rated pressure of 9.8bar for example 5bar. I thought with the decrease in pressure, the steam flow rate will also reduce. Am I right? And if so, is there a source i can go to and learn more? Thank you.
You are partially right. when you reduce the pressure usually the steam production is reduced and the fuel consumption too. But (there is always some "but") Imagine that you have a theoretically perfect thermally insulated boiler. You built up the pressure and close the main steam valve? What you have? You have a boiler under pressure (5 or 9 bar) which is not consuming fuel and the steam flow is zero. that means the steam flow, or better to use the steam production does not depends on pressure. If you open a small consumer of the steam (small heater) there will be steam production only to rebuild the preset pressure. If you open more or bigger consumer the steam flow will increase. As long as you do not know the consumption you can not determine the boiler's production.
Hi, Try using the energy balance around the boiler by considering it an open system.
Following equation may help you in such situations.
Q_dot = m_dot (delta_h_sensible + deltha_h_latent)
In this, the left side of the equation (Q_dot) is the amount of energy supplied to the boiler in terms of fuel consumption and can be found from (density x fuel flow rate x Heating value of the fuel). I hope this should help find your unknown m_dot on the right side of the above equation since you already know the two delta_hs from the thermo tables of water.
Hi, Try using the energy balance around the boiler by considering it an open system.
Following equation may help you in such situations.
Q_dot = m_dot (delta_h_sensible + deltha_h_latent)
In this, the left side of the equation (Q_dot) is the amount of energy supplied to the boiler in terms of fuel consumption and can be found from (density x fuel flow rate x Heating value of the fuel). I hope this should help find your unknown m_dot on the right side of the above equation since you already know the two delta_hs from the thermo tables of water.
If you know the fuel calorific value, CV, and mass, then with a certain efficiency of the boiler, Eyta, you can have an energy balance:
mfuel*CV*Eyta=Msteam*(hfg)
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