CFD mod­el­ing helps develop the best natural gas burners in the world

Com­pu­ta­tional fluid dynam­ics, CFD in short, is primar­ily used for numer­ical mod­el­ing of gas and liquid flows. CFD enables Oilon’s experts to sim­u­late dif­fer­ent pro­cesses, such as a burner’s oper­a­tion far ahead of cre­at­ing a phys­ical pro­to­type. This speeds up devel­op­ment, reduces costs, and results in a better product overall.

Nations around the globe are increas­ingly redu­cing their NOx emis­sions. This requires con­tinu­ous advances in com­bus­tion and boiler tech­no­logy, but there is also another factor to con­sider: which fuel to use. Oilon has made devel­op­ing Low-NOx com­bus­tion tech­no­logy a pri­or­ity. Another focus area are altern­at­ive fuels that meet the cri­teria for sus­tain­able devel­op­ment. In recent years, the company’s efforts have focused espe­cially on low-NOx solu­tions for natural gas. Let’s take a look at one example.

LN30 Ultra low NOx – a new family of burners

“This is where the magic happens, in the com­bus­tion head,” says Joonas Kat­telus, Oilon’s chief tech­no­logy officer. “We have recently intro­duced a new Monoblock product family, the LN30. When firing natural gas in these burners, we can achieve the record-​breaking Ultra Low NOx level, below 2.5 ppm (5 mg/Nm3). These are premix burners with a long, tubular com­bus­tion head. The smal­lest member in the family has a maximum capa­city of 900 kW (3.4 MMbtu/h) and the largest, 4.9 MW (18.6 MMBtu/h). These are indus­trial burners and occupy the lower-​to-average capa­city pos­i­tion in the Oilon product port­fo­lio.

“There have been other premix burners on the market for years already. However, what we are now offer­ing is con­sid­er­ably better than any pre­vi­ous models. For example, let’s compare our new solu­tion to premix mesh burner tech­no­logy where the fuel–air mixture is homo­gen­ized as much as pos­sible by feeding it into the furnace through a tight mesh. Our LN30 burners have no mesh; instead, we use a long tube with nozzles at one end for feeding the fuel and air into the furnace for com­bus­tion.”

Kat­telus explains that a mesh-​based burner requires extremely clean com­bus­tion air, as oth­er­wise impur­it­ies would clog up the mesh in the com­bus­tion head. In prac­tice, effect­ive fil­tra­tion is a must, and the filter itself would require fre­quent clean­ing. This tech­no­logy cannot be used in dusty envir­on­ments. The burners in the LN30 series have no filter; no filter is required, as there are no small open­ings prone to clog­ging.

Low NOx emis­sions at low resid­ual oxygen levels

“One sig­ni­fic­ant new char­ac­ter­istic of the LN30 series is its reduced resid­ual oxygen (O2) level,” Kat­telus con­tin­ues. “In tra­di­tional premix burners, the 9-ppm NOx limit can be achieved only with a 7–8% resid­ual oxygen level. With these burners, we can achieve this with an O2 level as low as 4–6%. At 6–8% O2, we can go as low as 5 ppm. Nat­ur­ally, our goal was to get the resid­ual oxygen level as low as pos­sible, as this improves effi­ciency.”

“We were able to fine-​tune our premix very close to per­fec­tion, res­ult­ing in a major boost in per­form­ance. The mixing process was developed entirely with CFD. By select­ing the right shape for the com­bus­tion head and the nozzles, and with proper nozzle place­ment, we managed to keep the flame extremely compact. The flame fits well even in a smaller furnace.”

Kat­telus elab­or­ates that a perfect premix will also reduce the risk of CO form­a­tion. Typ­ic­ally, when NOx levels go down, CO levels go up. With a perfect premix, all CO is con­sumed and the problem is avoided.

Another benefit of a long com­bus­tion head is that it pro­motes internal flue gas recir­cu­la­tion (IFGR) in the front section of the furnace. In this process, inert flue gas is mixed into the fuel–air mixture. This cools down the flame, redu­cing the form­a­tion of thermal NOx com­pounds and enabling the use of a lower O2 content in the flue gas.

“Tra­di­tion­ally, flue gas mixing has been achieved using external flue gas recir­cu­la­tion (FGR), where flue gas is fed into the furnace from the outside. However, external FGR has lim­it­a­tions that can be prob­lem­atic for some cus­tom­ers in certain situ­ations.”

Accord­ing to Kat­telus, Oilon has veri­fied its new burner family’s deliv­ery reli­ab­il­ity and per­form­ance with extens­ive labor­at­ory testing. The products have also been UL-​certified. The burner equip­ment for the first field case in the United States have been com­mis­sioned, and more deliv­er­ies are cur­rently under­way. Oilon has delivered LN30 products to other markets for some years already, with good results.

Oilon has patents pending for the new tech­no­logy in Europe and China. The tech­no­logy is already pat­en­ted in the USA.

CFD mod­el­ing is the key to excel­lent engin­eer­ing and devel­op­ment

For nearly 15 years, Oilon has util­ized CFD cal­cu­la­tion in burner engin­eer­ing and devel­op­ment. Today, CFD is one of the main devel­op­ment tools used at Oilon. In the early years, CFD cal­cu­la­tions took a long time to process and tended to deliver inac­cur­ate results, which meant that the tool was releg­ated to a sup­port­ive role. However, as pro­cessing power increased, com­pu­ta­tional models matured and the company’s knowhow expan­ded, CFD became more viable, and has now served several years as the company’s primary devel­op­ment tool.

“Today, we develop the com­bus­tion tech­no­logy used in our products largely using CFD sim­u­la­tion. Typ­ic­ally, the values we get are pretty much exactly the same as those we measure from the actual phys­ical pro­to­type,” Kat­telus says. “We used to make several pro­to­types during burner devel­op­ment, and testing each a long time. Now, thanks to CFD, we get better results faster and with fewer costs, even in a land­scape rife with increas­ingly strin­gent require­ments. On one hand, the boiler industry tends to keep furnace dimen­sions as small as pos­sible to reduce costs, and on the other, legis­la­tion aims to reduce emis­sion levels. There is a con­flict between these two, as a smaller furnace will increase NOx emis­sions.”

“Nat­ur­ally, both boiler per­form­ance and the amount of NOx emis­sions depend on both parts of the sum: the burner and the furnace. Emis­sion levels depend on several para­met­ers, but the main rule is that improv­ing the trans­mis­sion of heat from the flame to the furnace will always reduce NOx emis­sions. There are many ways to improve this, such as optim­iz­ing furnace dimen­sions, furnace cor­rug­a­tion, and min­im­iz­ing the use of refract­ory. CFD mod­el­ing allows us to work with boiler man­u­fac­tur­ers to ensure the best pos­sible result.”

Unique CFD know-​how and an excel­lent labor­at­ory

Over the years, Oilon has acquired an extens­ive exper­i­ence and a unique know-​how in util­iz­ing CFD mod­el­ing. This expert­ise is sup­por­ted by excel­lent labor­at­ory facil­it­ies in the company’s product devel­op­ment center. These two form a com­bin­a­tion that is hard to beat: meas­ure­ments from the labor­at­ory are used to develop CFD models, which, in turn, are veri­fied and further tested in the labor­at­ory. Accord­ing to Kat­telus, the company has the world’s most advanced natural gas com­bus­tion models, espe­cially when it comes to emis­sion mod­el­ing.