Q & A > Question Details
We find the crude heater tubes started slightly bowing towards the burner inside the radiation zone. The investigation drives my mind over the below written questions...
1. What can be the maximum height of the Fired heater's radiation zone (or) the maximum tube height allowed inside the radiation zone (vertical coil type) as per standard?
2. What is the efficient ratio which can be achieved between the radiation:convectional zone heat transfer(in percentage)? Its a balanced type heater and we could heat the combustion air up to 275 C max?
3. We use P9 material tubes inside the furnace (cylindrical-twin zone). We are puzzled as to why the bowing is towards the burner side? Why not towards the side and backwards?
4. What is the maximum pressure drop across the burners allowed? As we go increasing the throughput in varying the Fuel oil and Fuel gas burning, the skin temperature response in all the section of the heater is not uniform. So the heat flux variance is also expected. I would like to know the methods available to find the heat flux variance inside the radiation zone.
5. The burners (Low NOx/SOx) used are stretching over the design sometimes due to the lower inlet temperatures. Flue gas recirculation is also included in the design. What can be the problem when a burner is running over the design limits? We have oxygen, CO, NOx/SOx analysers but they don't seem to be reliable most of the time.
07/12/2011 A: Abraham Emamnuelxp, JC Equipments Pvt Ltd, emmanuelxp@gmail.com
Look at cooling tower
15/11/2011 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
Most probable reason for your 3 question is the wrong flame pattern from your burners. If the flame is not vertical and bushy, flame impingement on tubes will cause the bowing towards the flame. Check and correct the flame pattern of the burners close to the bowed tubes. Question 4: when the Fuel Oil and Fuel gas are simultaneously fired uniformity in flame distribution among all the burners shall be maintained. The flame lengths for the Fuel Gas flame and Fuel Oil flame are different, so the skin temperatures are going to be different. Fuel gas flames are notorious for burning near the convection bank where they can get some more oxygen from the unspent combustion air present in the flue gas(when the Flue gas sees some back pressure). Question 5: if a burner is forced to run over design for longer periods, the wear and tear of burner internals and consumption of those spares leading to higher opex will be the end result. Remember the internal include burner tiles. Tiles must be designed as a single block around the Fuel Gas risers. With some Low Nox burners (with joints in tiles) where Flue gas recirculation is considered, Fuel gas risers gets exposed to high temperatures and start cooling up if the Fuel Gas contains heavier components. So tile designs shall not allow the risers to pass thru joints.
14/11/2011 A: Mohamed S Banjar, Petrorabigh, Mohamed.Banjar@petrorabigh.com
1. Depends on the furnace size; generally the L/D ratio will range from 2.0 to 3.5
2. The split between radiant and convection duties can be obtained as function of the heat available in the products of the combustion at these temperatures
3. I believe the direction of the bowing with the draft direction in the fire box