The basic difference is that combustion is heating and no flames are produced whereas in

burning most of the energy is converted to light energy and this results in less heat energy as
compared to combustion.Combustionis a chemical process in which a substance reacts rapidly
with oxygen and gives off heat.

Stoichiometric or Theoretical Combustion is the ideal combustion process where fuel is burned
completely. A complete combustion is a process burning all the carbon (C) to (CO 2), all the
hydrogen (H) to (H2O) and all the sulphur (S) to (SO2).With unburned components in the
exhaust gas such as C, H2, CO, the combustion process is uncompleted and not
stoichiometric .To determine the excess air or excess fuel for a combustion system we starts
with the stoichiometric air-fuel ratio. The stoichiometric ratio is the perfect ideal fuel ratio
where the chemical mixing proportion is correct. When burned all fuel and air is consumed
without any excess left over.

Process heating equipment are rarely run that way. "On-ratio" combustion used in boilers and
high temperature process furnaces usually incorporates a modest amount of excess air - about
10 to 20% more than what is needed to burn the fuel completely. If an insufficient amount of
air is supplied to the burner, unburned fuel, soot, smoke, and carbon monoxide exhausts from
the boiler - resulting in heat transfer surface fouling, pollution, lower combustion efficiency,
flame instability and a potential for explosion.

Stable combustion conditions require right amounts of fuels and oxygen. The combustion
products are heat energy, carbon dioxide, water vapor, nitrogen, and other gases (excluding
oxygen). In theory there is a specific amount of oxygen needed to completely burn a given
amount of fuel. In practice, burning conditions are never ideal. Therefore, in practice more air
than ideal must be supplied to burn all fuel completely. The amount of air more than the
theoretical requirement is referred to as excess air. Natural gas-fired boilers may run as low
as 5 percent excess air.

Air-to-fuel ratio defines the amount of air needed to burn a specific fuel. The conventional fuels
used in a combustion process are: oil (#2, 4 and 6), diesel oil, gasoline, natural gas, propane,
and wood
For any combustion process there is a balance sought between losing energy from using too
much air, and wasting energy from running too richly. The best combustion efficiency occurs at
the optimum air-to-fuel ratio and controlling this provides the highest efficiency. In most
scenarios, a liquid and gas fuel burner achieves this desired balance by operating at 105% to
120% of the optimal theoretical air. For natural gas fired burners, the stoichiometric air
required is 9.4-11 ft.3 / 1.0 ft.3 of natural gas, or approximately an air-to-gas ratio of
approximately 10:1. This results in an excess oxygen level of 2%.

In the combustion zone, it is difficult to measure excess air. In the stack, however, it can be
easily measured using Oxygen analyzers. When operating with 5%-20% excess air, it would
correspond to a 1% to 3% oxygen measurement in the stack.

The ideal air-to-fuel relationship will vary at different operating loads. Tuning is the act of
establishing the desired air-to-fuel relationship under different operating conditions. This can
be accomplished when evaluating specifics in the stack: temperature, oxygen concentration, as
well as carbon monoxide and NOx emissions. To achieve complete combustion it is critical to
introduce air into the combustion chamber. Without it, the fuel will have partial or incomplete
combustion and the exhaust gases will contain some unburnt and partially burnt fuel. Assuming
we are evaluating a natural gas fed combustion process, the unburnt fuel components will be
carbon monoxide (CO), hydrogen (H2) as well as methane (CH4).

When determining the carbon monoxide content from the flue gas we are able to make
adjustments to the process operation because the CO content represents the unburnt fuel
which is wasted because of insufficient air. Alternatively, by measuring the O 2 in the stack gas
we are able to monitor the loss of energy from too much excess air.Oxygen and combustible
analyzers can provide continuous sampling and analysis of flue gases, making analyzing oxygen
and combustibles in the stack gases a way to maximize combustion efficiency. Optimum
combustion can be achieved at various air-to-fuel ratios to correspond with different operating
loads. This makes it challenging to use oxygen analyzers alone to control excess air.
Additionally, an uneven distribution of oxygen in the flue gas could result in oxygen level
variations.

If the flame isn’t just blue, the methane isn’t getting enough oxygen to burn completely, leaving
some of the carbon unburned. The flame will also not be as hot as a completely blue flame for
the same reason. The combustion process is extremely dependent on time, temperature, and
turbulence. Time is important to combustion because if a fuel is not given a sufficient amount
of time to burn, a significant amount of energy will be left in the fuel. Too much time to burn on
the other hand will produce very long flames, which can be a function of bad mixing. The
correct balance of time and mixing will achieve complete combustion, minimize flame
impingement (boiler maintenance hazard), and improve combustion safety. In addition, a
properly controlled combustion process strives to provide the highest combustion efficiency
while maintaining low emissions of harmful gases.

the sides of the triangle represent the interdependent ingredients needed for fire: heat, fuel
and oxygen. he sides of the triangle represent the interdependent ingredients needed for fire:
heat, fuel and oxygen.

The first requirement is to establish process variable signals by measuring the mass flow of the
fuel flow and combustion air flow rate. Since combustion is dictated by mass it is optimal to
measure mass flow rather than volumetric flow.Mass flow measurement of natural gas and
combustion air flow provides essential information for a facility to operate at maximum
efficiency and minimal emissions.

Coriolis flow meters provide a direct mass flow measurement based upon the deflection force
of the fluid moving through a vibrating tube. These meters are very accurate with high
turndown capabilities and are independent of fluid properties. They are also very expensive to
purchase and install, and are not suitable for larger pipe sizes.

Positive Displacement meters require fluid to mechanically displace components and

If the flame isn’t just blue, the methane isn’t getting enough oxygen to burn completely, leaving some of
the carbon unburned. The flame will also not be as hot as a completely blue flame for the same reason.