Process For Hydrotreatment Of Petroleum Fractions Including A Heat Pump Circuit

CATEGORY: HYDROTREATMENT
PATENT
Process For Hydrotreatment Of Petroleum Fractions Including A Heat Pump Circuit
United States Patent Application 20120145598
Inventors:
Giroudiere, Fabrice (Orlienas, FR)
Guillou, Florent (Ternay, FR)
Application Number: 13/316863
Publication Date: 06/14/2012
Assignee: IFP Energies nouvelles (RUEIL-MALMAISON CEDEX, FR)
Abstract:
This invention describes a new process for hydrotreatment or hydrodesulfurization of petroleum fractions that is thermally coupled to a process for amine treatment that employs a heat pump circuit that is established between a hot source located on the hydrotreatment process and a cold source located on the amine treatment system. The major effect of the process according to the invention is a reduction of CO2 emissions.
FIELD OF THE INVENTION
This invention relates to the field of the processes of refining and petrochemistry that employ distillation columns. This field is very vast, and, in a preferred manner, this invention applies to the more limited field of the processes for hydrotreatment or hydrodesulfurization of petroleum fractions.
This invention does not relate to the reaction or catalytic aspect of said processes but rather to the energy aspect thereof. The operations for physical separation of the components, such as distillation, are very energy-intensive operations. It is necessary to provide the energy that is necessary to bringing the mixture to a boil to separate its components. The efficiency of the separation, in the case of compounds that are similar in nature and are therefore difficult to separate, is generally enhanced by increasing the reflux of the column.
This increase of the reflux consists in recycling a more or less large part of the effluent that is produced at the top of the column to reinject it into the column in the liquid state. This is reflected by a supplementary energy to be provided at the bottom of the column to reboil this inventory of supplementary product.
Furthermore, the effluent at the top of the column is to be condensed to be recovered in liquid form.
This condensation can be done by employing a cooling tower, i.e., an exchanger that uses ambient air as a cooling fluid, which makes it possible for a low energy cost to dissipate excess heat into the atmosphere. The drawback of this type of exchanger is then that the heat is not enhanced. In other cases, this condensation by cooling tower is only partially possible because of the low temperature that is required, since the temperature of the fluid to be condensed cannot be less than that of the ambient air.
In the field of refining or petrochemistry, there is often recourse to vapor such as a coolant, in particular in the exchangers. In a typical refinery exchanger, generally superheated vapor condenses and yields its heat to the fluid to be heated. This vapor can be obtained from a dedicated heater in which, most often, the combustion of a hydrocarbon, such as natural gas, for example, is carried out. This combustion produces carbon dioxide (CO2), which will contribute to greenhouse gas (GHG) emissions of the site on which the distillation unit is installed.
In the case where the air is not adequate for cooling the effluent at the top of the column, it is necessary to have recourse to refrigeration by water, if it is used in a sufficient quantity, or by means of cold groups that, with a more or less significant energy expenditure, make it possible to use chilled water. This also gives rise to significant GHG emissions.
A solution for limiting these GHG emissions is, according to this invention, to install a heat pump circuit between the reboiler of the distillation column and the cooling tower, whose advantages are two-fold:

On the one hand, to cool the stream in question to temperatures that cannot be reached by a cooling tower system,
On the other hand, to upgrade the heat exchanged at the reboiler of the distillation column by raising its temperature level.
Another field of application of this invention is that of so-called feedstock-effluent exchangers that are often used for preheating the feedstock in various refining processes.
For the processes that rely on relatively high temperatures, in particular the processes that implement an exothermic reaction, there is often recourse to a feedstock-effluent exchange, with the feedstock being preheated by the hot effluent. However, this feedstock-effluent exchange is limited by the crossover phenomenon: it will not be possible to heat a feedstock beyond the temperature at which the effluent is available.
The installation of a heat pump in this case makes it possible to overcome this limitation by shifting the temperature levels beyond the crossover temperatures.
Examination of the Prior Art
The primary application of the heat pumps is the heating of either individual or industrial buildings, for example by the supply of heat to a hot water network, or the heating of a greenhouse for cultivating plants. With the principle of the heat pump being the transport of calories between two environments, from a “cold” environment to a “hot” environment, it is possible to operate while supplying cold. Thus, another application of the heat pumps is the air-conditioning of buildings.
In some cases, the effect that is generally sought by the installation of a heat pump is the energy savings and/or the economic gain relative to another heating method, an oil heater, for example. Actually, the heat pumps are characterized by a coefficient of performance levels that corresponds to the amount of energy that is necessary for the transport of an amount of energy between a hot environment and a cold environment, or vice versa. The smaller the temperature difference between the two environments, the better the performance level will be and the greater the energy savings will be.
This is the reason for which the heat pumps are advantageously used in heating/air-conditioning applications for which the temperature difference between the desired temperature of the building to be air-conditioned and that of the outside environment that will supply or absorb the calories (groundwater, atmosphere, lithosphere) is generally low, on the order of about 10 degrees Celsius.
In the case of refining and petrochemistry processes, and in particular for the diesel fuel hydrotreatment-type applications, the situation can be summarized in the following manner:
It is desired to desulfurize by hydrotreatment an initially hot diesel fuel feedstock, at approximately 130° C., in a process that partly operates at low temperature. Actually, the feedstock is to be cooled to approximately 50° C., but in contrast, large amounts of energy at approximately 130° C. are necessary for the regeneration of the solvent.
The temperature difference between, on the one hand, the cooled feedstock and, on the other hand, the temperature that is necessary to the regeneration of the solvent, is therefore approximately 80° C.
In a context of inexpensive energy, this is why this application is not considered advantageous from the standpoint of the performances of a heat pump, because the heat supply by means of a conventional heater by fossil hydrocarbon combustion is the simplest and most economical solution, with the heat of the feedstock to be cooled being dissipated directly into the atmosphere by cooling towers.
In contrast, in a context of tensions regarding energy, it is possible to prove that a heat pump is a profitable solution despite a fairly low performance coefficient, more particularly also in the case where there is interest in specific greenhouse gas emissions for which the heat pumps offer a good reduction potential.
This invention describes specifically the installing of a heat pump in this context and shows its energy advantage.
Actually, such an installation makes it possible both to upgrade a considerable amount of heat (which would be dissipated into the atmosphere according to the prior art), improving the efficiency of the cooling while reducing the required surface area at the cooling tower, and finally to provide the entirety of the heat required for the regeneration of the solvent with an advantageous carbon balance.
Free Full Text Source: http://www.freepatentsonline.com/y2012/0145598.html