NL2033569B1

NL2033569B1 - Flameless combustion of hydrocarbons

Info

Publication number: NL2033569B1
Application number: NL2033569A
Authority: NL
Inventors: Petrus Van Den Berg Johannus
Original assignee: Wte Tech B V
Priority date: 2022-11-18
Filing date: 2022-11-18
Publication date: 2023-09-27
Also published as: DE202023106803U1

Abstract

The present disclosure concerns a method of flameless combustion, comprising: preheating a combustion zone to above 800 °C; maintaining the temperature of the combustion zone at a temperature between 850 °C and 1400 °C; simultaneously injecting an oxidant and a hydrocarbon fuel mixture to the into the combustion zone, wherein the oxidant and the hydrocarbon fuel mixture are injected independently of each other from respective first and second locations; combusting the hydrocarbon fuel mixture without flames; and venting exhaust gasses, wherein the hydrocarbon fuel mixture combusts without flames by maintaining a furnace oxygen concentration of the combustion zone below 12% by volume and maintaining an exhaust gas recirculation rate of from 0 to 0.5.

Description

Flameless combustion of hydrocarbons

Field of the invention

The present invention relates to methods for and apparatus suitable for the flameless combustion of hydrocarbons.

Background of the invention

Hydrocarbons are used as a fuel source throughout the globe. These hydrocarbons are typically sourced from natural sources such as oil fields and gas fields. A significant portion of the extracted hydrocarbons are burnt (flared) at the source of extraction, for instance 80 billion cubic feet of hydrocarbons were either vented or flared in Saudi Arabia in 2020, which is equivalent to approximately 2% of Saudi Arabia’s natural gas production. Hydrocarbons are also typically flared during petroleum refining, where flaring is used as a safety release for waste and/or excess gas produced. Flaring excess gas is also conducted during hydrocarbon storage at fuel depots (storing chemicals, petroleum products [such as diesel, petrol, kerosene, heavy ship oil, etc.], biofuels, vegetable oils). During storage, to avoid overpressure build-up of volatile hydrocarbons within the storage tanks, volatile components are extracted and fed to a flare, where they are burnt. Flaring of hydrocarbons also occurs when storage tanks, such as oil depots or LPG tankers, need to be purged before being filled with new hydrocarbons.

Flaring hydrocarbons by traditional means was typically conducted with significant formation of nitrogen oxides, such as nitrogen oxide (NO) and nitrogen dioxide (NO.). These nitrogen oxides are often abbreviated as NO, compounds. NOx emissions are involved in the formation of smog, which is formed by reaction of NO, compounds with other volatile organic compounds (VOCs) in the atmosphere. NO, emissions are also a major source of acid rain.

Consequently, it is preferable from both a health and environmental perspective to reduce NOx emissions.

There are three major sources of NO, compounds that arise during combustion of hydrocarbons, which are typically referred to as: (i) “prompt NO”; (ii) “fuel NO”; and (iii) “thermal

NO”. “Thermal NO”, which arises from the “Zeldovich mechanism”, is the major source of NOx emissions from burning clean hydrocarbon sources, such as natural gas.

The three principle reactions that lead to the formation of NO, by thermal NO are as follows (in simplified form): (1) O+ N25 NO +N (2) N +02 = NO + N; and (3) N+ OH = NO + H.

These reactions are only significant at elevated temperatures, typically above 1400 °C.

Consequently, an early approach to reducing NOx emissions from flaring hydrocarbons was to reduce the flame temperature, such as by flame cooling. Alternative approaches involved “flame staging”, in which the reagents are introduced to a primary combustion zone under non- stoichiometric conditions, followed by cooling the resultant combustion products and then finally introduction to a secondary combustion zone. Since the 1988, “flameless combustion”, often referred to as “flameless oxidation” or by the trademark “FLOX”, has been investigated for reduced NO, formation. This flameless combustion was achieved with a furnace temperature of approximately 1000 °C and by pre-heating air to approximately 650 °C before introduction to the combustion zone. The characteristics of flameless combustion are that no flame is visible and minimal UV emission. It was found that such a flame could combust clean fuel with minimal NOx emissions and less than 1 ppm carbon monoxide content in the exhaust, which is indicative of complete combustion of the fuel. EP 0463218 A1 describes such flameless combustion.

Flameless oxidation allows for lower NO, generation than combustion staging

Commercial exploitation of flameless combustion systems has slowly grown since the mid 1990's, being exploited with clean fuels in steel mills (as heat sources for silicon steel strip lines, annealing lines and pickling lines), Stirling engines and gas turbines.

Research has established that homogeneous mixing of the fuel and air/ oxidant within the combustion zone are of importance for forming stable flameless oxidation zones, as this avoids “hot spot” formation within the combustion zone where the temperature exceeds 1425 °C at which NO, forms rapidly. One way this is achieved is by pre-mixing fuel/air or fuel/oxidant streams before introduction to the oxidation zone/furnace. Whilst this ensures good mixing and thereby more homogeneous combustion, it normally imposes limitations on: (i) what fuels can be used; (ii) what impurities the fuel can comprise; and (iii) what concentrations such fuels can be used to avoid forming mixtures prone to explosion and/or deflagration. For example, (i) if methane is used as the fuel: (ii) the methane fuel may only comprise up to 15% by volume hydrogen; and (iii) methane must be diluted below the lower flammability limit (LFL) of 4.4 volume% in air.

Flameless combustion requires a minimum threshold temperature of around 850 °C.

Below this temperature incomplete oxidation occurs. Temperatures in the combustion zone above threshold temperature are relatively easy to maintain when clean fuels can be reliably provided at a sufficient rate. However, when fuels are provided with occasional, short periods where insufficient fuel is actually provided to the combustion zone, incomplete combustion occurs. For fuels that cannot be reliably provided at a sufficient rate, by which is meant fuel which can generally be provided at a sufficient rate with short periods of a few seconds where it cannot, this issue can be partially addressed by using a combustion zone filled with a porous matrix of high heat capacity ceramics. The porous matrix retains sufficient heat to restart flameless combustion after the short periods without sufficient fuel provision. The disadvantages of such complicated structures are that they suffer from rapid fouling of the pathways, inability to cope with extended deficiencies in fuel provision, high pressure differences across the matrix and difficulties in maintenance. A further disadvantage is that the high heat capacity of the matrix makes it hard to detect insufficient fuel provision by way of a drop in temperature within the combustion zone. Such systems also employ pre-mixing of fuel and air/oxidant, and so inherit the limitations of such premixing.

A goal of the disclosure of the present application is to provide a method and apparatus that allows for flameless combustion of hydrocarbon fuels: (i) whose composition may change over time; (ii) that may comprise high impurity volumes such as hydrogen; (iii) at high volume percent to the combustion zone and/or (iv) at a rate insufficient to maintain spontaneous flameless combustion.

Summary of the disclosure

In view of the above discussion, a first aspect of the present disclosure relates to a method of flameless combustion, comprising: 0 preheating a combustion zone to above 800 °C; (ii) maintaining the temperature of the combustion zone at a temperature between 850 °C and 1400 °C; (iii) simultaneously injecting an oxidant and a hydrocarbon fuel mixture to the into the combustion zone, wherein the oxidant and the hydrocarbon fuel mixture are injected independently of each other from respective first and second locations (iv) combusting the hydrocarbon fuel mixture without flames; and (v) venting exhaust gasses, wherein the hydrocarbon fuel mixture combusts without flames by maintaining a furnace oxygen concentration of the combustion zone below 12% by volume and maintaining an exhaust gas recirculation rate of from 0 to 0.5.

A second aspect of the present disclosure relates to a flameless combustion apparatus suitable for the method of flameless combustion of the previous aspect, comprising: - a furnace comprising a combustion zone; - at least one FLOX burner, the FLOX burner comprising a first injection port, the first injection port comprising a first nozzle configured to allow injection of a first hydrocarbon fuel mixture and a second nozzle configured to allow injection of an oxidant;

- at least one start-up burner capable of operating under FLOX and flame combustion conditions comprising a second injection port, the second injection port comprising a third nozzle configured to allow injection of a first ancillary fuel and a fourth nozzle configured to allow injection of an oxidant; - a means of measuring a combustion temperature; - an exhaust port (stack); - wherein the first and second injection ports are arranged in parallel so as to allow provision of the first hydrocarbon fuel mixture and oxidant to the FLOX burner; and - wherein the third and fourth injection ports are arranged in parallel so as to allow provision of the first ancillary fuel mixture and oxidant to the start-up burner.

A third aspect of the present disclosure relates to a method for combusting Boil-Off Gas (BOG) comprising hydrocarbons, the method comprising: - collecting BOG comprising at least one hydrocarbon from at least one hydrocarbon storage tank; - delivering the collected BOG to a combustion apparatus suitable for performing the method of the first aspect; and - combusting the BOG under flameless conditions according to a method according to any embodiment of the first aspect.

A fourth aspect of the present disclosure relates to a method for combusting Residual

Gas and/or Liquid (RGL) comprising hydrocarbons, the method comprising: - bringing a hydrocarbon storage tank into fluid communication with a combustion apparatus suitable for performing the method of any embodiment according to the first aspect; - delivering a gas comprising residual gas and/or liquid from the hydrocarbon storage tank to the combustion apparatus; - when the temperature of the combustion zone of the combustion apparatus exceeds 850 °C, combusting the residual gas and/or liquid under flameless conditions according to a method according to any embodiment according to the first aspect; - controlling the supply of residual gas and/or liquid to the combustion zone to maintain a temperature above 850 °C so as to maintain flameless combustion in the combustion zone - when the maximal supply of residual gas and/or liquid to the combustion zone of the combustion apparatus becomes insufficient to maintain a temperature of above 850 °C, providing auxiliary fuel to the combustion zone of the combustion apparatus and combusting both: (i) the auxiliary fuel; and (ii) the residual gas and/or liquid under flameless conditions according to a method according to any embodiment of the first aspect.

A fifth aspect of the present disclosure relates to a system suitable for combusting 5 Residual Gas and/or Liquid (RGL) comprising: - at least one hydrocarbon storage tank; and - a combustion apparatus suitable for performing the method of any embodiment of the first aspect, wherein the hydrocarbon storage tank(s) are connected to the combustion apparatus by means allowing the hydrocarbon storage tanks to be brought into fluid communication with the combustion apparatus.

A sixth aspect of the present disclosure relates to method for degassing a hydrocarbon storage tank, wherein the method comprises the following steps: - pumping out any liquid from the hydrocarbon storage tank until less than 5% of the hydrocarbon storage tank by volume is filled with hydrocarbon liquid; - bring hydrocarbon storage tank into liquid communication with an intermediate storage tank; - vaporizing residual hydrocarbon liquid in the hydrocarbon storage tank; - allowing vapourised hydrocarbon to move from the hydrocarbon storage tank to the intermediate storage tank; - optionally condensing and/or compressing vapourised hydrocarbon in the intermediate storage tank; - purging the hydrocarbon storage tank with an inert gas; - delivering the purging gas from the hydrocarbon storage tank to: (i) the storage tank, and/or (ii) a combustion apparatus suitable for performing the method of any embodiment according to the first aspect; - delivering at least some of the purging gas comprising the hydrocarbon to the combustion apparatus; - when the temperature of the apparatus exceeds 850 °C, combusting the gas delivered to the apparatus under flameless conditions according to a method according to any embodiment according to the first aspect; - when the temperature of the apparatus is below 850 °C, providing auxiliary fuel as a co-feed to the purging gas comprising the hydrocarbon and combusting the auxiliary fuel and gas delivered to the apparatus under flameless conditions according to a method according to any embodiment according to the first aspect.

A seventh aspect of the present disclosure relates to a system suitable for degassing a hydrocarbon storage tank of a ship comprising: - an intermediate storage tank; - a combustion apparatus suitable for performing the method of any aspect according to the first aspect; - means to bring the hydrocarbon storage tank of a ship into fluid communication with the intermediate storage tank; and - means to bring the hydrocarbon storage tank of a ship into fluid communication with the combustion apparatus and/or means to bring the intermediate storage tank of a ship into fluid communication with the combustion apparatus.

Short Description of the Figures

Figure 1 depicts a schematic lay out for a method for combusting Boil-Off Gas (BOG) comprising hydrocarbons for three connected storage tanks.

Figure 2 depicts a representative off gas rate for a number of connected storage tanks over a year.

Figure 3 depicts an apparatus according to the second aspect of the invention.

Figure 4 depicts the variation of combustion zone temperature and O: concentration by volume versus off gas hydrocarbon fuel mixture flow variation from 50 to 910 kg/hr.

Figure 5 depicts the simulated variation of combustion zone temperature and O2 concentration by volume under simulated drop out of hydrocarbon fuel mixture off gas flow and incoming auxiliary LPG fuel gas.

Figure 6: depicts the simulated variation of combustion zone temperature and O2 concentration by volume versus off gas hydrocarbon fuel mixture upon drop out of hydrocarbon fuel mixture off gas flow and incoming auxiliary LPG fuel gas.

Definitions and Abbreviations

Recirculation rate, Ky. The recirculation rate, Kv, is defined as follows:

Kv = Me / (MF + Ma), where: (i) Me is the mass of recirculated exhaust gas; (ii) Mr is the mass of the hydrocarbon fuel; and (iii) Ma is the mass of combustion air

Detailed Description of the Invention

A first aspect of the present disclosure relates to a method of flameless combustion, comprising:

MH preheating a combustion zone to above 800 °C; (ii) maintaining the temperature of the combustion zone at a temperature between 850 °C and 1400 °C; iii) simultaneously injecting an oxidant and a hydrocarbon fuel mixture into the combustion zone, wherein the oxidant and the hydrocarbon fuel mixture are injected independently of each other from respective first and second locations; (iv) combusting the hydrocarbon fuel mixture without flames; and (v) venting exhaust gasses, wherein the hydrocarbon fuel mixture combusts without flames by maintaining a furnace oxygen concentration of the combustion zone below 12% by volume and maintaining an exhaust gas recirculation rate of from 0 to 0.5.

One advantage of this method is that it allows for flameless combustion of hydrocarbon fuel mixtures that have very high operational turndown ratios. Therefore, the method can be suitably used for flameless combustion of hydrocarbon fuel mixtures that: (i) vary over time in terms of hydrocarbon composition; (ii) flow rate/mass transfer; and/or (iii) vary over time in terms of individual hydrocarbon concentration. Varying hydrocarbon composition, flow rate and/or hydrocarbon concentration typically results in changes in different combustion enthalpies and/or combustion entropies. This advantageously allows for flameless combustion of hydrocarbon fuel mixtures without analysis of exact hydrocarbon composition and concentration to operate, such as boil-off gas.

A further advantage of the present method is that it generates less noise than traditional flaring methods.

Yet another advantage of the present method is that it operates at lower oxygen concentrations (below 12%) in the combustion chamber than known flameless oxidation systems. This advantageously allows for significantly higher concentrations of hydrocarbons in the hydrocarbon fuel mixture to be safely combusted, in the range of 1.5 to 15% by volume of the fuel mixture, without exceeding the lower explosion limits.

An advantage of simultaneously separately injecting an oxidant and a hydrocarbon fuel mixture into the combustion zone, wherein the oxidant and the hydrocarbon fuel mixture are injected independently of each other from respective first and second locations is that pre- mixing of the hydrocarbon fuel mixture and oxidant can be avoided before introduction to the combustion chamber. This advantageously allows for significantly higher concentrations of hydrocarbons in the hydrocarbon fuel mixture to be safely combusted, in the range of 1.5 to 15% by volume of the fuel mixture, without exceeding the lower explosion limits.

Preferably, the method is one in which the oxidant is pre-heated before injection into the combustion zone. This pre-heating of the oxidant advantageously allows yet higher operational turndown ratios to be employed.

Preferably, the method is one in which the hydrocarbon fuel mixture is pre-heated before injection into the combustion zone. This pre-heating of the hydrocarbon fuel mixture advantageously allows yet higher operational turndown ratios to be employed.

Preferably, the method is one wherein the hydrocarbon fuel mixture is selected from a boil-off gas, a residual gas or liquid, a hydrocarbon storage purge gas or any combination thereof.

Preferably, the method is one in which the temperature of the furnace is maintained at a temperature of from 850 to 1200 °C by either: - Introducing cooling air with a temperature of below 40°C to the furnace ; and/or - Introducing an auxiliary fuel to the furnace.

One advantage of this preferable embodiment is that greater control of the temperature in the combustion zone can be obtained by adding cool (<40 °C) air and/or adding auxiliary fuel to the furnace.

More preferably, the auxiliary fuel is selected from propane, Liquefied Petroleum Gas (LPG), Natural Gas (NG), refinery fuel gas or any combination thereof.

Preferably, the method is one wherein the furnace oxygen concentration is maintained at from 3% to 12% by volume, preferably from 3% to 10% by volume.

Maintaining an oxygen concentration above 3% by volume advantageously minimizes

CO formation.

Preferably, the method is one wherein the furnace temperature is maintained at a temperature of from 800-1400 °C, preferably of from 850 to 1200 °C, more preferably of from 900-1100 °C.

Preferably, the method is one wherein the method comprises a first step of pre-heating the combustion zone to above 800 °C using an auxiliary fuel.

Preferably, the method is one, wherein the auxiliary fuel is selected from methane, ethane, propane, butane, natural gas, any ignitable other hydrocarbon or flammable gaseous feed (e.g. H2) or any combination thereof, more preferably selected from methane, ethane,

propane, butane, natural gas, any other hydrocarbon, hydrogen or any combination thereof, most preferably selected from methane, ethane, propane, butane.

Preferably, the method is one wherein the (pre-heated) oxidant is introduced to the oxidation zone at a velocity of at least 40 m/s, preferably at a velocity of at least 50 m/s.

Preferably, the method is one wherein the first hydrocarbon fuel is introduced to the oxidation zone at a velocity of at least 40 m/s, preferably at least 50 m/s, more preferably at least 80 m/s,

Preferably, the method is one wherein the first hydrocarbon fuel is provided to the combustion zone at 0.8 to 50 megajoules per normal cubic metre (MJ/Nm?®), preferably 1.0 to 30

MJ/Nm?3, more preferably 1.5 to 20 MJ/Nm?,

Preferably, the method is one wherein the first hydrocarbon fuel is a hydrocarbon off- gas.

Preferably, the method is one wherein the first hydrocarbon fuel comprises hydrogen.

Preferably, the hydrocarbon fuel mixture is introduced at a flow rate of at least 50 m/s.

This may be measured using a dP measurement over the injector. This advantageously allows for minimizing the risk of flare-backs.

A second aspect of the present disclosure relates to a flameless combustion apparatus suitable for the method of flameless combustion of the previous aspect, comprising: - a furnace comprising a combustion zone; - at least one FLOX burner, the FLOX burner comprising a first injection port comprising a first nozzle configured to allow injection of a first hydrocarbon fuel mixture and a second nozzle configured to allow injection of an oxidant; - at least one start-up burner capable of operating under FLOX and flame combustion conditions comprising a second injection port, the second injection port comprising a third nozzle configured to allow injection of a first ancillary fuel and a fourth nozzle configured to allow injection of an oxidant; - a means of measuring a combustion temperature; and - an exhaust port (stack); - wherein the first and second injection ports are arranged in parallel so as to allow provision of the first hydrocarbon fuel mixture and oxidant to the FLOX burner; and - wherein the third and fourth injection ports are arranged in parallel so as to allow provision of the first ancillary fuel mixture and oxidant to the start-up burner.

The apparatus according to the second aspect may advantageously allow for the method of the first aspect to be performed, with all attendant advantages.

The configuration of injection ports allows the first hydrocarbon fuel mixture and first auxiliary fuel to be provided to separate burners (FLOX burner and start-up burner) capable of

FLOX combustion. This configuration advantageously allows the apparatus to maintain an operational temperature that minimizes NO, emissions despite low hydrocarbon concentrations in the first hydrocarbon fuel mixture. Therefore, the configuration allows the apparatus to possess a high turndown ratio. This configuration also advantageously allows the apparatus to maintain an operational temperature that minimizes NOx emissions in the case of temporary interruption of first hydrocarbon fuel mixture provision. This configuration advantageously allows for the omission of thermal buffering.

The configuration of first and second injection ports are arranged in parallel advantageously allows for the apparatus to operate without pre-mixing of the first hydrocarbon fuel mixture before introduction to the apparatus.

Preferably, the apparatus has a plurality of FLOX burner units. This advantageously allows the apparatus to possess an even higher turndown ratio.

Preferably, the apparatus has a means of measuring the pressure within the combustion zone.

Preferably, the apparatus comprise a means of measuring the O2 concentration within the combustion zone. Such means advantageously allows the apparatus to be operated with greater combustion control.

Preferably, the apparatus comprise a heat exchanger. More preferably, the heat exchanger is configured to allow heat to be transferred from the exhaust to: (i) the hydrocarbon fuel mixture; (ii) the oxidant; (iii) the ancillary fuel; (iv) generate steam for energy combustion; and/or (v} any combination thereof. This advantageously allows for greater fuel efficiency when the apparatus is operated with low hydrocarbon concentration in the hydrocarbon fuel mixture.

This also advantageously allows for a lower exhaust temperature, which may be required for safe operation in areas at risk of hydrocarbon leaks, such as LPG tanks or on LPG tankers.

Preferably, the flameless combustion apparatus comprises a start-up burner. The start- up burner is configured to allow the combustion chamber to be brought up to a temperature of at least 850 °C. More preferably, the flameless combustion apparatus comprises start-up burner selected from a propane burner, a Liquefied Petroleum Gas (LPG) burner, a Natural Gas (NG) burner, a refinery fuel gas burner or any combined fuel burner thereof.

Preferably, the method comprises the additional step of: - purging the storage tank with an inert gas and delivering the hydrocarbon comprising purging gas to the combustion apparatus; - when the temperature of the combustion zone of the combustion apparatus exceeds 850 °C, introducing the hydrocarbon comprising purging gas to the combustion zone to combust the hydrocarbons within the purging gas under flameless conditions according to a method according any embodiment of the first aspect; - controlling the supply of hydrocarbon comprising purging gas to the combustion zone to maintain a temperature above 850 °C so as to maintain flameless combustion in the combustion zone; and - when the maximal supply of purging gas to the combustion zone of the combustion apparatus becomes insufficient to maintain a temperature of above 850 °C, providing auxiliary fuel to the combustion zone of the combustion apparatus and combusting both: (i) the auxiliary fuel; and (ii) the hydrocarbons of the purging gas under flameless conditions according to method according to the first aspect.

Preferably, the method is conducted with the proviso that if flameless combustion is not possible, the purging gas is passed through a flare.

Preferably, the purging gas is selected from nitrogen, argon or a mixture thereof.

A fifth aspect of the present disclosure relates to a system suitable for combusting

Residual Gas and/or Liquid (RGL) comprising: - at least one hydrocarbon storage tank; and - a combustion apparatus suitable for performing the method of any embodiment of the first aspect, wherein the hydrocarbon storage tank(s) are connected to the combustion apparatus by means allowing the hydrocarbon storage tanks to be brought into fluid communication with the combustion apparatus.

A sixth aspect of the present disclosure relates to method for degassing a hydrocarbon storage tank , wherein the method comprises the following steps: - pumping out any liquid from the hydrocarbon storage tank until less than 5% of the hydrocarbon storage tank by volume is filled with hydrocarbon liquid; - bringing the hydrocarbon storage tank of vessel into fluid communication with an intermediate storage tank; - vaporizing residual hydrocarbon liquid in the hydrocarbon storage tank; - allowing vapourised hydrocarbon to move from the hydrocarbon storage tank to the intermediate storage tank; - optionally condensing and/or compressing vapourised hydrocarbon in the intermediate storage tank; - purging the hydrocarbon storage tank with an inert gas; - delivering the hydrocarbon comprising purging gas from the hydrocarbon storage tank to: (i) the storage tank, and/or (ii) a combustion apparatus suitable for performing the method of any embodiment according to the first aspect; - delivering at least some of the purging gas comprising the hydrocarbon to the combustion apparatus; - when the temperature of the combustion zone of the combustion apparatus exceeds 850 °C, combusting the gas delivered to the apparatus under flameless conditions according to a method according to any embodiment according to the first aspect; - controlling the supply of hydrocarbon comprising purging gas to the combustion zone to maintain a temperature above 850 °C so as to maintain flameless combustion in the combustion zone; and - when the maximal supply of purging gas to the combustion zone of the combustion apparatus becomes insufficient to maintain a temperature of above 850 °C, providing auxiliary fuel to the combustion zone of the combustion apparatus and combusting both: (i) the auxiliary fuel; and (ii) the hydrocarbons of the purging gas under flameless conditions according to method according to the first aspect.

The present aspect of the invention is particularly advantageous for removing residual hydrocarbons from the purging gas as it can cope with the extreme changes in hydrocarbon content of the purging gas. Purging hydrocarbon storage tanks with inert gases typically result in a purge gas that initially contains a high hydrocarbon content, dominated by highly volatile hydrocarbons. As the purging process continues, the overall hydrocarbon content diminishes over time and composition becomes increasingly dominated by less volatile hydrocarbons. The present aspect advantageously allows nitrogen to be used as the purging gas without excessive NO, emissions. The present aspect also advantageously obviates the need for real- time analysis of overall hydrocarbon concentration and/or hydrocarbon composition in the purge gas. Preferably the purging gas is selected from nitrogen, argon or a mixture thereof, more preferably, the purging gas is nitrogen.

A seventh aspect of the present disclosure relates to a system suitable for degassing a hydrocarbon storage tank comprising: - an intermediate storage tank; - a combustion apparatus suitable for performing the method of any aspect according to the first aspect; - means to bring the hydrocarbon storage tank into fluid communication with the intermediate storage tank; and - means to bring the hydrocarbon storage tank into fluid communication with the combustion apparatus and/or means to bring the intermediate storage tank into fluid communication with the combustion apparatus.

Detailed Description of the Figures

The disclosure will now be discussed with reference to the figures, which show preferred exemplary embodiments of the subject disclosure.

Figure 1 depicts a schematic lay out for a method for combusting Boil-Off Gas (BOG) comprising hydrocarbons. In this example there are three hydrocarbon storage tanks [T1, T2 and T3]. In the depicted method, BOG comprising at least one hydrocarbon is collected from at least one of the hydrocarbon storage tanks [T1, T2 and/or T3]. This is depicted by arrows [A1,

A2 and/or A3]. The BOG comprising at least one hydrocarbon may be collected from one, two or all of the tanks simultaneously or sequentially. The BOG comprising at least one hydrocarbon is optionally passed [A4] through a pre-treatment plant [P1], such as an AC filter, which allows: (i) residual H2S and/or (ii) condensed hydrocarbons to be fully or partially removed from the

BOG. The collected BOG comprising at least one hydrocarbon is delivered to a combustion apparatus suitable for performing the method of the first aspect [C1]. This is depicted by the arrow [A5]. The BOG is combusted under flameless conditions according to a method according to any embodiment of the first aspect.

Figure 2 depicts a representative off gas rate for a number of connected storage tanks over a year. The typical flow pattern is shown for 8800 hours (flow rate on the y-axis, with graduations in 100 m3/hour, time on the x-axis, with graduations in 1000 hours), with every 4 hours corresponding to a data point. The average flow is estimated at 145,2 m3hour and the maximum flow-rate was estimated at 839 m3/hour.

Figure 3 depicts a non-limiting example of the line-up (PFD) of an apparatus according to the second aspect of the invention. In this non-limiting example, the combustion chamber is a square combustion chamber with a length of 5 m, a height of 2 m and a width of 2 m. The combustion chamber is designed with one start-up burner, eight high velocity vent gas injectors and four probes for (cooling) air injection. Two LPG or propane probes will be installed for injection of auxiliary fuel.

Figure 4 depicts the simulated variation of combustion zone temperature and O2 concentration by volume versus off gas hydrocarbon fuel mixture flow variation from 50 to 910 kg/hr for unit start-up conditions.

The x-axis is time in minutes, from 2 to 29 minutes in graduations of 4 minutes. There are four y-axes, which read from left to right, are as follows: 1. hydrocarbon fuel mass flow (“LCV4” in kg/h), 0 to 1250 kg/h in graduations of 250 kg/h; 2. Temperature of the combustion zone (°C), 0 to 1500 °C, in graduations of 300 °C; 3. Computed mole fraction O2 (in %) from 0.0250 to 0.160, in graduations of 0.0250; and 4. Auxiliary fuel mass flow (propane, denoted “Fuel206”, in kg/h), from 0 to 20 kg/h, in graduations of 4 kg/h.

The lines, starting from top to bottom as they intersect the y-axis, are as follows: a. Temperature, with a starting value of 900 °C; b. Auxiliary fuel flow rate, with an initial value of 2.7 kg/h; c. Computed mole fraction O2 , with an initial value of 3.5%; and d. Hydrocarbon fuel mass flow, with an initial value of 0.

In the first shaded zone (reading from left to right), the hydrocarbon fuel starts to be provided to the combustion zone, and the amount of auxiliary fuel provided starts to be reduced {and goes to zero at approximately 7 minutes). As the hydrocarbon fuel combusts, it provides sufficient energy to the combustion zone to maintain the temperature above the 850 °C required for flameless oxidation (FLOX).

In the second shaded zone (reading from left to right), a drop in hydrocarbon fuel supply was simulated. This lead to a rapid drop in temperature to approximately 900 °C and spike in the oxygen concentration to approximately 12%. To maintain the temperature above 850 °C and the oxygen concentration in the safe region of below 12%, auxiliary fuel was rapidly provided.

The auxiliary fuel combusted under FLOX conditions, providing sufficient energy to the combustion zone to maintain a temperature above 850 °C, and consuming sufficient oxygen to maintain the oxygen concentration below 12%.

In the third shaded zone (reading from left to right), hydrocarbon fuel supply was stopped, due to the low mass flow of the hydrocarbon fuel supply. Correspondingly, the supply to auxiliary fuel was increased.

Figure 5 depicts the simulated variation of combustion zone temperature and O2 concentration by volume under simulated of the start of off gas feeding to the combustion chamber.

The x-axis is time in minutes, from 3575 to 3640 minutes in graduations of 5 minutes.

There are four y-axes, which read from left to right, are as follows: 1. hydrocarbon fuel mass flow (“LCV4” in kg/h), O to 1260 kg/h in graduations of 252 kg/h; 2. Computed mole fraction O2 from 0.0250 to 0.160, in graduations of 0.0250; 3. Auxiliary fuel mass flow (propane, denoted “Fuel206”, in kg/h), from G to 20 kg/h, in graduations of 4 kg/h; and 4. Temperature of the combustion zone (°C), 0 to 1500 °C, in graduations of 300 °C.

The lines, starting from top to bottom as they intersect the y-axis, are as follows: a. Temperature, with a starting value of 900 °C; b. Auxiliary fuel flow rate, with an initial value of 3,1 kg/h; c. Computed mole fraction Oz, with an initial value of 5%; and d. Hydrocarbon fuel mass flow, with an initial value of 0.

A rapid increase in hydrocarbon fuel supply was simulated (at approximately 3568 minutes), from O to 950 kg/h. This is representative of opening a value to a partially filled hydrocarbon storage tank at ambient temperatures. The rapid provision of hydrocarbon fuel leads to a rapid increase in temperature of the combustion zone to 1030 °C, a rapid switch off of auxiliary fuel supply, and a rapid increase in oxygen concentration from around 5% to around 12%. A rapid stop in hydrocarbon fuel supply was simulated (at approximately 3595 minutes, zone A), from 950 kg/h to 0. This is representative of closing a value to a partially filled hydrocarbon storage tank at ambient temperatures. The rapid cessation of the provision of hydrocarbon fuel leads to a rapid decrease in temperature of the combustion zone from approximately 1000 °C to below 850 °C and a rapid increase in oxygen concentration from around 12% to around 14%. This occasioned an almost instantaneous switch-on of auxiliary fuel supply at around 3595 minutes, resulting in a very short-lived period where the temperature dipped below 850 °C of approximately 120 s. This is much shorter than comparable methods, and this method correspondingly should result in far less NOx generation.

Figure 8: depicts the simulated variation of combustion zone temperature and O2 concentration by volume versus off gas hydrocarbon fuel mixture upon drop out of hydrocarbon fuel mixture off gas flow and incoming auxiliary LPG fuel gas

There are four y-axes, which read from left to right, are as follows: 1. Temperature of: (i) the combustion zone (°C); and (ii) the stack (°C), from 0 to 1455 °C, in graduations of 291 °C; 2. Computed mole fraction O2 from 0.090 to 0.160, in graduations of 0.016; and 3. Hydrocarbon fuel mass flow (“LCV4” in kg/h), O to 1260 kg/h in graduations of 252 kg/h.

The lines, starting from top to bottom as they intersect the y-axis, are as follows: a. Temperature of the combustion zone (“Furnace T7); b. Computed mole fraction O2 , with an initial value of approximately 0.128; c. Temperature of the stack (“Stack T”); and d. Hydrocarbon fuel mass flow, with an initial value of 0.

List of reference numerals 1 Flameless combustion apparatus 2 Furnace 3 Combustion zone 4 First injection port 5 First nozzle configured to allow injection of a first hydrocarbon fuel 6 Second injection port 7 Means of measuring a combustion temperature, such as a thermocouple 8 Exhaust port 9 Fan 10 Valve

11 Solenoid valve 12 Ai inlet filter 13 Flap for cooling air 14 Actuator motor 15 Pressure switch 16 Filter 17 Ball valve 18 Solenoid with pressure reducer 19 Valve 20 First FLOX burner 21 Second FLOX burner 22 Start-up burner capable of operating under FLOX and flame combustion conditions 23 Oxygen sensor 24 Flap 25 Linear flow control 26 Air 27 Hydrocarbon fuel 28 Exhaust gas 29 Auxiliary fuel

Examples

The following, non-limiting examples illustrate the products and processes according to the disclosure.

Example 1 — Process simulation of a method according to the present disclosure

An apparatus according to Figure 3 was used in the simulation. The simulation was based on the schematic set up of Figure 1. Mixtures of off gas and air under minimum, low, average and maximum conditions as detailed in Table 1 were used to model the performance of the method according to the first aspect of the invention, using an apparatus according to the second aspect of the invention.

The lower heating values for the minimum and low mixtures are calculated as 5.5 and 7.7 MJ/Nm3, respectively. The Heat- and Mass-Balance (H&M Balance) for the average case of

Table 1 was calculated. It was determined that starting with 6,6 kmol/hr of LCV gas (= air- hydrocarbon off gas mixture from tank, see Table 1) 12,9 kmol/hr cold air is required for temperature control and oxygen supply. In effect the total furnace is operating at 10 %v Ox, which is a safe oxygen content for any sudden variation in hydrocarbon content. Combustion temperature is estimated at 1000 °C.

The maximum case has been simulated resulting in a calculated H&M Balance. It was determined that with 26.4 kmol/hr tank off gas mixture 110,6 kmol/hr cold air is required for temperature control and oxygen supply. Also for this case we estimate the effective combustion temperature at 1000 °C.

It is estimated that the method according to the first aspect results in NOx emissions of less than 25 mg/Nm? and less than 12 parts per million volume (ppmv). It is estimated that when the method is performed wherein the furnace oxygen concentration is maintained at from 3% to 12% by volume, this results in: (i) NOx emissions less than 25 mg/Nm?® and less than 12 ppmv; (ily CO emissions under 20 mg/Nm3 and less than 16 ppmv; and (iii) total organic compound emissions of less than 2 mgC/Nm? and less than 4 ppmv.

Component Minimum Low Average Maximum Units

Ze Eger

Tago

Aro Tg otal Flow 0.07 BATT Ess re gor

Table 1. Tank off gas — gas flow and composition.

Example 2 — Dynamic process simulation of a method according to the present disclosure

In view of the high flow variations that are characteristic for tank off gas flow patterns [Figure 2], a series of dynamic simulations were performed to quantify the system response upon rapid changes in off gas feed flow.

Key elements of respective parts of the extended Process Flow Diagram (PFD), are as follows:

1. The tank off gas feed system includes a gas pressure booster and flow control. In our simulations we have worked on basis of an initial pressure (ex-tank) of 103 kPa, to be adjusted to actual level. 2. The auxiliary fuel gas, which can be Propane or LPG (optionally Natural Gas, NG, can be used), ensures fuel control for the step of preheating a combustion zone to above 800 °C and supplementary fuel addition in case of very lean off gas composition and for maintaining furnace temperature above 800 °C during zero flow. 3. The oxidant was selected from combustion air. The supply of fresh air was controlled for: (iy combustion; (ii) O2 concentration and (iii)for temperature control. 4. The burner section and combustion chamber included a set of 8 hydrocarbon fuel mixture gas burners (Figure 3). Each burner was modelled as having a minimum capacity of 45 kg/hr and a maximum capacity of 140 kg/hr. In addition, one start-up burner was modelled for pre-heating the combustion chamber to above 800 °C from cold start-up or for providing additional heat to maintaining the temperature above 850 °C during flameless combustion. For the zero flow cases two additional Propane or LPG probes were modelled. For the dynamic simulation only the 8 LCV gas burners are relevant. 5. The dynamics of the unit operation were simulated with a continuous change of the inlet gas flow from 50 to 910 kg/hr, increase from 50 to 910 kg/hr within 5 minutes, followed by a sudden decrease of the inlet flow back to 50 kg/hr, drop to 50 kg/hr within 1 minute. 6. In Figure 5 the system response over a period of 10 minutes is plotted. For key parameters like furnace temperature and O2 concentration in flue gas we see changes as follows: - with the rapid flow increase the O: concentration varies between 12,9 %v (initial) and 11,7 %v (lowest point), while the combustion zone temperature varies between 977 and 1044 °C, both well under control; and - with the sudden drop in hydrocarbon fuel mixture inlet gas flow, we calculated that the combustion zone temperature briefly decreased to 902 °C, while the oxygen concentration goes up to 13 % by volume followed by a coming down to 12 % by volume in the subsequent stabilization. The full dynamics show an effective control of the key parameters for the combustion chamber, with that ensuring full and stable combustion through the whole sweep of hydrocarbon fuel mixture gas inflow from low to high and back to low.

In an analogous simulation over a longer period (65 minutes) the impact of zero off gas flow in combination with incoming auxiliary fuel gas (LPG in our example) was analysed. As is shown in Figure 6 with the incoming LPG gas the combustion zone temperature is well controlled within the requirements of the method. In response to reduction of air supply for controlling the combustion zone temperature (reduction of flow due to lower furnace temperature) the O2 level in the combustion chamber can drop to 5 % by volume, which is still in the right window for full combustion under flameless combustion conditions. Hence, the present method, when optionally comprising the step in which the temperature of the furnace is maintained at a temperature of from 850 to 1200 °C by introducing an auxiliary fuel to the furnace is simulated as advantageously allowing for flameless combustion that can endure temporary supply shocks of the hydrocarbon fuel mixture without emitting undesirably levels

NO, or CO.

Claims

Conclusions

1. Method for carrying out combustion without viam formation, comprising: ® preheating a combustion zone to a temperature higher than 800 °C; (ii) maintaining the temperature of the combustion zone at a value between 850°C and 1400°C; (ii) simultaneously injecting an oxidant and a hydrocarbon fuel mixture into the combustion zone, wherein the oxidant and the hydrocarbon fuel mixture are injected independently of each other from first and second locations, respectively; (iv) burning the hydrocarbon fuel mixture without flame formation; and (v) the removal of combustion gases, whereby the hydrocarbon fuel mixture is burned without flame formation by maintaining an oxygen concentration in the combustion zone of less than 12% by volume and by maintaining a recirculation ratio for the combustion gases which lies between 0 and 0.5.

A method according to claim 1, wherein the oxidant is preheated before being injected into the combustion zone.

Method according to claim 1 or 2, wherein the fuel mixture of hydrocarbons is preheated before being injected into the combustion zone.

4. Method according to any one of the preceding claims, wherein the fuel mixture of hydrocarbons is selected from a boil-off gas, a residual gas or a residual liquid, a purging gas for a storage of hydrocarbons, or from any combination of the foregoing.

5. Method according to any one of the preceding claims, wherein the temperature of the oven is maintained at a value between 850 °C and 1200 °C, by: introducing air into the oven at a temperature lower than 40 °C C; and/or e introduce an auxiliary fuel into the furnace.

Method according to any one of the preceding claims, wherein the concentration of oxygen in the oven is maintained at a value between 3% by volume and 12% by volume, and preferably between 3% by volume and 10% by volume.

7. Method according to any one of the preceding claims, wherein the temperature in the oven is maintained at a value between 800 °C and 1400 °C, which is preferably between 850 °C and 1200 °C, and which is preferably between 850 °C and 1200 °C. is between 900 °C and 1100 °C.

Method according to any one of the preceding claims, wherein the method comprises a first step of preheating the combustion zone to a temperature higher than 800°C, wherein this preheating is carried out by using an auxiliary fuel.

9. Method according to any one of the preceding claims, wherein the auxiliary fuel is selected from methane, ethane, propane, butane, natural gas, or from any other hydrocarbon or flammable gaseous feed, or any combination of the foregoing, wherein the auxiliary fuel is even better selected is of methane, ethane, propane, butane, natural gas, or of any other hydrocarbon, hydrogen, or any combination of the foregoing, and wherein the auxiliary fuel is preferably selected from methane, ethane, propane, butane.

Method according to any one of the preceding claims, wherein the (preheated) oxidant is introduced into the oxidation zone at a speed of at least 40 m/s, and preferably at a speed of at least 50 m/s.

A method according to any one of the preceding claims, wherein the first hydrocarbon fuel is introduced into the oxidation zone at a speed of at least 40 m/s, and preferably at a speed of at least 50 m/s.

A method according to any one of the preceding claims, wherein the first hydrocarbon fuel is supplied to the combustion zone at 0.8 megajoules per normal cubic meter to 50 megajoules per normal cubic meter (MJ/Nn3), preferably at 1.0 MJ/ Nm? up to and including 30 MJ/Nm?, and preferably 1.5 MJ/Nm? up to and including 20 MJ/Nm3.

A method according to any one of the preceding claims, wherein the first hydrocarbon fuel is a hydrocarbon off-gas.

A method according to any one of the preceding claims, wherein the first hydrocarbon fuel comprises hydrogen.

Apparatus (1) for carrying out combustion without flame formation, suitable for a method for carrying out combustion without flame formation, according to any one of the preceding claims, comprising: s an oven (2) comprising a combustion zone (3); e at least one FLOX burner (20), the FLOX burner comprising a first injection port (4), the first injection port (4) comprising a first manifold (5) configured to enable the injection of a first hydrocarbon fuel, as well as a second manifold configured to allow the injection of an oxidant; e at least one start-up burner (22) capable of operating under FLOX and flame combustion conditions, said start-up burner comprising a second injection port (6), said second injection port (6) comprising a third manifold configured to enable injection to make a first auxiliary fuel, as well as a fourth manifold configured to allow the injection of an oxidant; e means for measuring a combustion temperature (7); and e a discharge port (8); « wherein the first and second injection ports are arranged in parallel, in such a way as to enable the supply of the first hydrocarbon fuel mixture and of the oxidant to the FLOX burner; and e wherein the third and fourth injection ports are arranged in parallel, in such a manner as to enable the supply of the first auxiliary fuel mixture and optionally of the oxidant to a FLOX burner.

Apparatus according to claim 15, wherein the second injection port and the furnace are configured in such a way as to allow combustion without flame formation of the first auxiliary fuel with a combustion gas recovery ratio between 0 and 0.5.

17. Method of burning boil-off gas (BOG) comprising hydrocarbons, the method comprising: e collecting BOG comprising at least one hydrocarbon from at least one hydrocarbon storage tank; delivering the collected BOG to a combustion device suitable for carrying out a method according to any one of claims 1 to 15; and e burning the BOG under conditions that do not give rise to viam formation, by using a method according to any one of claims 1 to 15.

18. Method for burning Residual Gas and/or Residual Liquid (RGL) containing or comprising hydrocarbons, wherein the method comprises: e bringing a storage tank for hydrocarbons into fluid communication with a combustion device suitable for carrying out a method according to any of claims 1 to 14; e delivering to the combustion zone a gas that comprises residual gas and/or residual liquid and that originates from the hydrocarbon storage tank; e controlling the supply of residual gas and/or residual liquid to the combustion zone, in order to maintain a temperature higher than 850 °C, in order to maintain combustion without flame formation in the combustion zone s when the maximum supply of residual gas and/or residual liquid to the combustion zone of the combustion zone becomes insufficient to maintain a temperature higher than 850 °C, the supply of auxiliary fuel to the combustion zone of the combustion device, and the burning of (i) the auxiliary fuel and of ( ij) the residual gas and/or the residual liquid under conditions that do not give rise to viam formation, according to any of claims 1 to 14.

A method according to claim 18, wherein the method comprises the additional step of: e purging the storage tank using an inert gas, and delivering the purging gas comprising the hydrocarbons to the combustion zone; e when the temperature of the combustion zone of the combustion zone exceeds 850 °C, introducing into the combustion zone the purge gas containing the hydrocarbons in order to burn the hydrocarbons contained in the purge gas, under conditions that do not give rise to to viam formation, according to a method according to one of the embodiments of the first aspect; e controlling the supply to the combustion zone of purge gas containing the hydrocarbons in order to maintain a temperature higher than 850 °C, in order to maintain combustion without vitreous formation in the combustion zone; and e when the maximum supply of purge gas to the combustion zone of the combustion device becomes insufficient to maintain a temperature exceeding 850°C, supplying auxiliary fuel to the combustion zone of the combustion device, and burning (i) the auxiliary fuel and of (ij) the hydrocarbons of the purge gas under conditions that do not give rise to flame formation, according to a method according to the first aspect.

20. Method according to claim 18 or 19, with the provision that, if combustion without flame formation is impossible, the purging gas is passed through a torch.

A method according to any one of claims 18 to 20, wherein the purge gas is selected from nitrogen, argon, or from a mixture of the foregoing.

22. System suitable for burning residual gas and/or residual liquid (RGL), comprising: at least one tank for the storage of hydrocarbons; and e a combustion device suitable for carrying out a method according to any one of claims 1 to 14, wherein the tank(s) for the hydrocarbons is or are connected to the combustion device by means that make it possible to connect the storage tank for the hydrocarbons to bring hydrocarbons into fluid communication with the combustion device.

23. Method for degassing a hydrocarbon storage tank, the method comprising the following steps: e removing any liquid from the hydrocarbon storage tank using a pump until less than 5% of the volume of the storage tank for the hydrocarbons is filled with a hydrocarbon liquid; e bringing the storage tank for hydrocarbons into fluid communication with an intermediate storage tank; e evaporating residual hydrocarbon liquid in the hydrocarbon storage tank; + allowing vaporized hydrocarbons to move from the hydrocarbon storage tank to the intermediate storage tank; e the optional condensation and/or compression of vaporized hydrocarbons in the intermediate storage tank; e purging the storage tank for the hydrocarbons using an inert gas; e delivering the inert gas comprising hydrocarbons originating from the storage tank for the hydrocarbons to (i) the storage tank and/or (ij) to a combustion device suitable for carrying out a method according to any embodiment according to the first aspect;

e delivering to the combustion device at least part of the purge gas comprising the hydrocarbons; e when the temperature of the combustion zone of the combustion device exceeds 850°C, burning the gas delivered to the device, under conditions that do not give rise to flame formation, according to a method according to one of the embodiments according to the first aspect; e controlling the supply to the combustion zone of the purge gas containing the hydrocarbons in order to maintain a temperature higher than 850 °C, in order to maintain combustion without flame formation in the combustion zone; and e when the maximum supply of purge gas to the combustion zone of the combustion device becomes insufficient to maintain a temperature above 850 °C, the supply of auxiliary fuel to the combustion zone of the combustion device, and the burning of ( i) the auxiliary fuel and (ii) the hydrocarbons from the purge gas, under conditions that do not give rise to viam formation, according to a method according to the first aspect.

The method of claim 23, wherein the purge gas is selected from nitrogen, argon, or from a mixture of the foregoing.

25. System suitable for degassing a hydrocarbon storage tank of a ship, comprising: e an intermediate storage tank; e a combustion device suitable for carrying out a method according to any one of claims 1 to 14; s means for placing the hydrocarbon storage tank of a ship in fluid communication with the intermediate storage tank; and means for placing the hydrocarbon storage tank of a ship in fluid communication with the combustion device, and/or means for placing the intermediate storage tank of a ship in fluid communication with the combustion device.