Fuel equivalent steam

In most cases, Qf ei is calculated based on the lower heating value of fuel. G,- is quantified in different units according to specifications in the marketplace, namely, Btu/h for fuel, Ib/h for steam, and kWh for power. Thus, specific FE factors can be developed as follows based on this general definition of fuel equivalent. Energy are required for making boiler feed water (BFW), condensate and cooling water. The FE factors for these utilities will be discussed in Chapter 3. 

To reveal the significance of FE calculations, let us assume a process receives 20klb/h of HP steam in which lOklb/h comes from a boiler with efficiency of 75% and another lOkIb/h from a boiler with efficiency of 85%. Obviously, the fuel required or fuel equivalent for the same amount of HP steam, that is, 10 klb/h, by the two boilers is very different The fuel equivalent from the boiler with 85% efficiency is 15.35 MMBtu/h, resulting in FE factor of 1.535 MMBtu/klb. The fuel equivalent... 

In previous discussions, some assumptions of fuel equivalent factors were made for power and steam. You may ask What is the basis for making these assumptions How do you determine fuel equivalent values for power and steam in your plant Let us consider the calculation of fuel equivalent for power first. 

Calculate the fuel equivalent values for the steam headers in Figure 3.3. 

Solution. To determine the fuel equivalent for steam headers, different steam flow paths must be identified, which could have an influence on the fuel equivalent for the steam. 

In general, high-pressure steam is defined as steam produced from steam generators, mainly boilers. The fuel equivalent of high-pressure steam ean be derived as ... 

In most eases, multiple boilers are used. In this case, equation (3.11) can be applied to derive the weighted average of fuel equivalent for eombined HP steam going to the HP header ... 

Path 1 40klb/h of MP extraction Ifom TG-1001 with specific steam rate wihp-mp at 35.6 klb/MWh. The fuel equivalent for the MP steam exhaust can be calculated ... 

What about the FE for vented LP steam In this case, FElp should also be calculated based on the path from which this vented LP steam is generated. This is because a certain amount of fuel equivalent is consumed to make the LP steam no matter whether it is used or vented or not. For vented LP steam, the economic value is zero but FE is not. 

FE fuel equivalent amount of fuel at the source to make a unit of energy utility (power, steam)... 

Both enthalpy and work-based steam pricing methods rely on thermodynamic laws as the basis. Cooper (1989) argued that the steam pricing should reflect economic reality. Since the operating cost for a steam system mainly consists of fuel burned for steam generation. Cooper (1989) proposed to use the concept of fuel equivalent (FE) as the basis for steam pricing. In this method, the ratio of FE for steam at different pressures is used to derive the steam prices in placement of the ratios of enthalpy and availability. 

It is common that steam turbines are connected to steam headers. Therefore, it is logical to take power generation into account when steam price is determined. In reality, when the turbine is offline while the motor is online to run the rotating equipment, the power is imported but fuel for steam is saved. On the other hand, when the turbine is turned online while the motor is offline, import power is saved but at the expense of fuel for steam. To reflect the relative price comparison of fuel and power, the price equivalent efflciency (PEE) for power generation is defined as the price ratio ... 

There is only 2% (63%-61%) improvement from the steam system operation in Figure 18.4. The net fuel equivalent for the improved steam system with power import of 12.7 (20-7.3) mw is... 

Compared with the net fuel equivalent of 351 MMBtu/h for the steam system in Figure 18.4, use of the most efficient turbines can only achieve energy savings of 14 MMBtu/h (351 337). This indicates that the optimized existing steam system... 

Raw material usages per ton of carbon disulfide are approximately 310 m of methane, or equivalent volume of other hydrocarbon gas, and 0.86—0.92 ton of sulfur (87,88), which includes typical Claus sulfur recovery efficiency. Fuel usage, as natural gas, is about 180 m /ton carbon disulfide excluding the fuel gas assist for the incinerator or flare. The process is a net generator of steam the amount depends on process design considerations. 

Hot corrosion is a rapid form of attack that is generally associated with alkali metal contaminants, such as sodium and potassium, reacting with sulfur in the fuel to form molten sulfates. The presence of only a few parts per million (ppm) of such contaminants in the fuel, or equivalent in the air, is sufficient to cause this corrosion. Sodium can be introduced in a number of ways, such as salt water in liquid fuel, through the turbine air inlet at sites near salt water or other contaminated areas, or as contaminants in water/steam injections. Besides the alkali metals such as sodium and potassium, other chemical elements can influence or cause corrosion on bucketing. Notable in this connection are vanadium, primarily found in crude and residual oils. 

An alternative cost also became apparent from the case studies. If the mean hourly steaming rate in kilograms is multiplied by 2.25, it produces a figure roughly equivalent to the annual operating costs in pounds, excluding the cost of fuel. 

---