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# Hydrotreater - cost of +1 deg inlet temp

## Hydrotreater - cost of +1 deg inlet temp

(OP)
Dear all,

I'm looking for a way to quantify the cost to increase a hydrotreater inlet temp by 1 degree.

Specifically, I am at a loss of how to correlate the megwatts per ton of feed required to heat up +1 degree to the cost of the associated fuelgas per ton reactor feed.

I am not working in a refinery so do not have access to site economics. I realise that the cost depends heavily on the refinery configuration, but would appreciate to see a few examples or read other tips as how to quantify and calculate an order of magnitude.

Any useful comment would be greatly appreciated.
Replies continue below

### RE: Hydrotreater - cost of +1 deg inlet temp

Hopefully there are some "useful comments" here.

Many hydrotreaters (HTU) process hot feed. For cold feed - all HTUs would have feed/effluent exchange so the feed might come in from cold storage at say 100 deg F, and be heated to say 500 deg F mostly by feed/effluent heat exchange, and then, after the reactor, exchange back down to 100 deg F for a high pressure separation. So you might increase gas firing for the 1 degree (a simple calculation), then have to cut most of the gas back when the heat exchange comes around. I assume not much exotherm in your HTU. If there is much exotherm you might end up with no extra fuel gas. So I guess, for me, the question is too general. I suppose you would also have to include shorter catalyst life in your calculation due to the increased reactor temperature, unless the increase was just part of a normal unit cycle (regen to regen or catalyst change cycle). I would like to see other responses to the question.

HAZOP at www.curryhydrocarbons.ca

### RE: Hydrotreater - cost of +1 deg inlet temp

I suggest to do the following:
the heat duty that you have to give to the feed is:
feed flow rate (kg/h)*specific heat (kca/kg°C)*temperature difference (°C).
In your case the temperature difference is 1°C.
In this way you calculate X kcal/h that you must provide.
I assume that this X must be given by the furnace. The furnace has an efficiency, for example 0.85. This means that the duty given by the furnace fuel is X/0.85. Knowing the fuel calorific power (FCP), you can evaluate the fuel flow rate: flow rate = (X/0.85)/FCP
In this way you calculate the furnace flow rate increase in order to give 1°C more. At this point if you know the fuel price you can estimate the cost.
let me know

### RE: Hydrotreater - cost of +1 deg inlet temp

I agree with sottocutaneo except that you will need to take into account the % vaporized and the latent heat of vaporization of the process fluid in the heat balance, if there phase change in the fired-heater.

A simpler way to calculate the cost of the extra degree celcius is to divide the quantity of Fuel Gas by the difference between the process fluid outlet and inlet temperatures. This directly gives you the amount of fuel gas necessary to increase the process fluid temperature to 1°C (ton/°C). Then you will need the fuel gas price ($/ton). Multiply the two to have the cost of the extra degree celcius ($/°C).

Note that this cost will correspond to a set of parameters (such as draft and %O2) and any change in these parameters will affect the calculated cost.

"We don't believe things because they are true, things are true because we believe them."

### RE: Hydrotreater - cost of +1 deg inlet temp

A way to estimate the fuel gas price is to multiply the price of the most valuable fuel of your plant (for instance a fuel that you can export or sell to a power plant) by FCP of Fuel Gas/10000 (in kcal/kg).

"We don't believe things because they are true, things are true because we believe them."

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