### Boiler Turndown

• Boiler turndown is the ratio between a boiler’s maximum and minimum output. Depending on the burner’s design, it may have a turndown ratio between 4:1 and 10:1 or even higher.
• A 4:1 turndown means the boiler’s minimum operating load is 25% of the boiler’s full capacity (100% capacity divided by 4).
• A 10:1 turndown means the minimum operating load is 10% of the full load capacity (100% capacity divided by 10).

### Why is Boiler Turndown Ratio Important?

• Turndown ratio is important for boilers that are required to operate at a wide variation of capacities. A boiler with a higher turndown ratio will usually handle fluctuating loads more efficiently than one with a low turndown.
• A boiler’s burner will modulate or “turn down” as the demand for hot water or steam decreases, in an attempt to meet only the required load. The turndown ratio tells you the minimum output the boiler can handle before turning off and then cycling on and off frequently.
• If the demand goes below the burner’s minimum turndown, the boiler will cycle off until there’s more demand. This results in the system cycling on, running for a brief period and then cycling off again. Every time this happens, the boiler must go through a pre-purge, a firing interval and then a post-purge.
• For example, a 500-horsepower boiler with 10:1 turndown will modulate down to 50 horsepower before turning off and then cycling on and off. At a 4:1 turndown, the same capacity boiler would only modulate down to 125 horsepower. If the application has a minimum load of 50 horsepower, the 10:1 boiler could accommodate that without shutting off, but the 4:1 boiler would have to use multiple short cycles to maintain the load.

### How Turndown Ratio Affects Boiler Efficiency

For applications with a low load demand, a low turndown ratio will generally result in lower boiler efficiency and frequent on-off cycling. When the system has to cycle on and off frequently, it can also cause a number of costly issues:

### Selecting the Right Turndown Ratio

Correct boiler sizing and turndown ratio go hand in hand. In many cases, facilities may opt for a single over-sized boiler to accommodate the maximum load for the application and any expansion in the future. However, if load demand fluctuates widely, a high-capacity system may not be able to handle the minimum load without frequent cycling. On the other hand, it wouldn’t make sense to choose a boiler with a high turndown if it’s not sized to meet the highest load demand.

### Differences between MC/MC-C and ME/ME-C engines

The electrohydraulic control mechanisms of the ME engine replace the following components of the conventional MC engine: Chain drive for camshaft Camshaft with fuel cams, exhaust cams and indicator cams Fuel pump actuating gear, including roller guides and reversing mechanism Conventional fuel pressure booster and VIT system Exhaust valve actuating gear and roller guides Engine driven starting air distributor Electronic governor with actuator Regulating shaft Engine side control console Mechanical cylinder lubricators. The Engine Control System of the ME engine comprises: Control units Hydraulic power supply unit Hydraulic cylinder units, including: Electronically controlled fuel injection, and Electronically controlled exhaust valve activation Electronically controlled starting air valves Electronically controlled auxiliary blowers Integrated electronic governor functions Tacho system Electronically controlled Alpha lubricators

### Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole  is lesser in size than the corresponding circular hole. More over it is prime concern to have a  smoothed generous radius at the corners to eliminate stress concentration. Hence other  geometrical shapes like rectangle and square are ruled out.  To compensate for the loss of material in the shell due to opening, a doubler ring has to be  provided around the opening. The thickness of the ring depends on the axis length along the  dirrection in which the stresses are maximum and the thickness of the shell. It is important to  align the minor axis along the length of the vessel, as the stress in this direction is  maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t=  thickness of the shell plating  Circumferential stress: Pd/4t  More over a considerable material and weight saving is achieved as minor is along the  direction of maximum stress.

### Shell Expansion Plan

It is a two dimensional drawing of a three dimensional surface of the ship’s hull form. This plan is very useful for the following information:It is used for marking the location of a hull Damage on this plan by identifying the strake number , letter and frame number so that the exact location of the damage and also suggested repairs are marked in a localised copy. The shell expansion can be used for finding areas of painting surfaces such as topside, boot topping and bottom areas by applying Simpsons rules directly.  In the shell expansion the vertical scale used is different from the horizontal scale and a suitable adjustment has to be made when calculating areas. This becomes useful in solving disputes concerning areas of preparation and painting. It gives information on the thickness of the original strake which is indicated by the number in the circle shown in the strake.  The quality of steel used is also shown by letters A,B,D E and AH, BH,DH, EH.