JPH0674885B2 - How to recycle unburned carbon as solid fuel - Google Patents

Description

TECHNICAL FIELD The present invention relates to solid combustion of unburned carbon generated in a combustion process of petroleum-based hydrocarbons, for example, a combustion process of petroleum coke or a synthetic gas production process by partial oxidation of hydrocarbons. As to how to recycle.

Conventional technology Conventionally, "C" heavy oil has been widely used as an industrial boiler fuel, but the cost has increased significantly since the oil shock, and for the past few years, conventional "C" heavy oil has been used as a boiler fuel for coal and petroleum coke. Alternatively, it has come to be used by converting it into a solid or semi-solid fuel such as asphalt at room temperature. However, there are technical limitations in converting a "C" heavy oil boiler to coal-fired, and when using petroleum coke or asphalt as a fuel for the boiler, unburned carbon (hereinafter referred to as a suit) generated during boiler combustion. Is a problem.

In other words, when a boiler that used to use "C" heavy oil was converted to petroleum coke fuel, 2-3 gr / Nm ^{3 in the} combustion gas was used.
A small amount of dust is emitted. This also changes depending on the amount of "C" heavy oil that is co-firing with petroleum coke, but specifically, the co-firing ratio of petroleum coke and "C" heavy oil is 65:35 to 90:10. 80:20 for the most common range
Is. That is, petroleum coke 80 and "C" heavy oil by weight ratio
In many cases, 20 and 20 are mixed and burned, and the amount of petroleum coke combustion ash (hereinafter referred to as EP suit) (mixture of unburned carbon and ash) at this time is 1% to 4.
5% (weight) range, generally 2% to 3.5% (weight)
Is.

This EP suit remaining in the combustion gas is separated by an electric dust collector or the like provided in the flue and discharged to the outside of the boiler system. In addition, it is generally treated as industrial waste, and the cost and land for disposal are regarded as problems.

Therefore, it has been proposed to mold a part of the EP suit as it is or to form it into pellets for reburning for a special purpose such as a cement firing kiln or a fluidized bed boiler (Japanese Patent Laid-Open No. 58-200921).

However, in order to reburn it with a general industrial boiler,
EP suits have 10% volatile content compared to ordinary petroleum coke
It is as low as below, while the ash content is as high as 10% or more, and it is not appropriate to use it as fuel as it is. In particular, since the amount of ash is large, the amount of deposition on the surface of the heat transfer tube of the boiler is significant, which causes damage to the heat transfer tube and reduces the thermal efficiency of the boiler, which is not preferable.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Accordingly, the present invention achieves that i) ash is removed from this EP suit as much as possible, ii) volatile matter is added to carbon separated from ash to make it as flammable as possible. , It is intended to be reused as a solid fuel for general industrial boilers.

Means for Solving the Problems Based on the above object, the inventors of the present invention have made unburned gas generated in the combustion process of petroleum hydrocarbons, in particular, the combustion process of petroleum coke or the synthesis gas production process by partial oxidation of hydrocarbons. When a mixture of carbon and ash is made into a water suspension and unburned carbon is granulated using a petroleum-based binder, unburned carbon that has a strong affinity with the petroleum-based binder is granulated and has an affinity with the petroleum-based binder. The ash that is hydrophilic and does not exist remains in water, and as a result it is possible to recover the unburned carbon from which the ash has been separated and removed, and to confirm that the present invention can be reused as a solid fuel. It came to completion.

In this way, the separation and production of carbon granules (hereinafter referred to as pellets) and ash when the EP suit is separated and processed will vary depending on the amount of binder used and the amount of carbon and ash in the EP suit. About 1.1-1.2 times as much pellet and 0.05-0.15 times as much ash as EP suit.

Although the present invention is the first time to focus on removing ash from the EP suit and reusing it as a solid fuel, a technique for continuously granulating unburned carbon generated by partial oxidation of petroleum hydrocarbons and Techniques for separating unburned carbon have already been established, and the present invention can also be carried out using these techniques. About these technologies,
39-21502, JP 44-19507, JP 48-
It is described in detail in Japanese Patent No. 41248 and Japanese Utility Model Publication No. 53-39737.

The present invention can be specifically achieved by the following method, for example. That is, unburned carbon generated in the synthesis gas production process by partial oxidation of hydrocarbons by the shell gasification method developed by Shell Group is removed from the synthesis gas by a spray tower using a solid-liquid separator. The washing water discharged from the tower is a black suspension containing fine carbon particles. Commercially available "C" heavy oil, for example, is added as a binder to this suspension of washing water and unburned carbon, and the mixture is stirred. Since the unburned carbon is essentially lipophilic in nature, the binder is adsorbed on the surface of the unburned carbon particles and the surface is covered with the binder. The coated particles collide with each other by stirring, the particles are aggregated by adhesion, further grow, are compacted, granulated and separated from water.

The pellets of the invention can also be used in admixture with other solid fuels such as petroleum coke or coal.

The mixing ratio with other solid fuel varies depending on the type of solid fuel to be co-firing, the type of combustion furnace, combustion conditions such as furnace temperature, furnace oxygen concentration, fuel particle size, etc.
It is suitable to mix it in the range of 96 to 98% by weight, preferably 96 to 98% by weight.

Examples of analytical values of petroleum coke EP suit and pellet used in the present invention are as follows.

The pellets are measured values (% by weight) after drying at 105 ° C. ± 2, 4 hours.

Ash content 2.3%, volatile content 19.7%, fixed carbon 78.0% (ash content is Fe,
It is a metal component composed mainly of Ni, V, and SiO ₂ .

Total calorific value 8.240Kcal / kg Moisture 1.9% (Adhesion moisture before drying) Ash meltability Softening point 1,280 ° C, melting point 1,320 ° C, melting point 1,330 ° C Examples The present invention will be described below with reference to Examples. , But is not limited to this.

[A] Relationship between unburned rate and residence time Electrostatic collection of a mixture (EP suit) of unburned carbon of less than 10 μm and ash containing 7.20% of volatile matter and 80.34% of fixed carbon produced by combustion of petroleum coke It collects with a device, separates unburned carbon and ash with a separator, granulates unburned carbon into pellets, and conducts a combustion test using a combustion device (one-dimensional flow type combustion device, small laminar flow furnace). Then, the flammability of various fuels was evaluated from the change over time in the unburned rate (1-X) (X is the burn rate).

The analytical values of the samples used in the combustion test are as follows.

1) Petroleum coke combustion ash (EP suit) Ash content 12.46% Volatile content 7.20% Fixed carbon 80.34% C 82.0% H 0.81% Density [g / cm ³ ] 1.880 2) Pellet (EP suit + heavy oil) Ash content 1.64% (16.39%) ) Volatile content 15.33% (13.03%) Fixed carbon 83.03% (70.58%) C 91.97% H 2.09% Density [g / cm ³ ] 1.794 Note 1) In the case of pellet combustion, the ash content as a tracer is as low as 1.64%. , And 15% by weight of ash (Taiwan charcoal burning ash) was added in advance in order to avoid sticking between particles.

The figures in parentheses are the analytical values (calculated values) after adding ash.
Is.

Combustion ash used as a tracer is Pacific coal combustion ash collected by a cyclone by combustion in a turbulent flow furnace (coal combustion amount, 5 kg / hr), and has ash content of 99.81% and unburned content of 0.19%.

3) A mixture of 2% pellets and 98% petroleum coke Ash 0.55% (15.47%) Volatile 1.28% (1.08%) Fixed carbon 98.17% (83.45%) Density [g / cm ³ ] 1.652 Note 2) Within () Is the analytical value (calculated value) after adding 15% by weight of ash. The analysis value of petroleum coke is JIS M 8812.
Method, ash content 0.53%, volatile content 0.99, fixed carbon 9
8.48%.

The combustion test conditions are as follows.

Furnace temperature (gas temperature) (Tg) 1200 ° C Oxygen concentration in the furnace 21% (air) Fuel particle size Petroleum coke combustion ash: used for the test pellets: crushed in a mortar pellets 2% and petroleum coke 98% Mixture of -325 mesh, 100% Petroleum coke: -325 mesh, 100% Note 3) For pellets, 15% by weight of Pacific charcoal combustion ash was mixed to prevent sticking, and then crushed in a mortar.
Also, in the case of a mixture of 2% pellets and 98% petroleum coke, similarly, crushed powder of -325 mesh, 100% was used.

The measurement results are shown in FIG. 1 [relationship diagram between unburned rate (1-X) and particle retention time (t _R )].

From Fig. 1, when comparing the mixture of 2% pellets and 98% petroleum coke (curve 3) with petroleum coke (curve 4), the ignition delay time was about 100 mS and after ignition, There is no big difference in the burning rate, and it is considered that mixing the petroleum coke with 2% pellets (by weight) has almost no effect on the overall burning reaction rate.

Also, comparing the pellet (curve 2) and petroleum coke combustion ash (EP suit) (curve 1), the pellet has better ignitability because it contains a binder (heavy oil) (ignition delay about 50-60 mS ), The gradient of the curve burning rate after ignition is gentle, and the burning rate is lower than that of the EP suit. This is because pellets are likely to re-aggregate even after crushing, and thus have a wider particle size distribution than other samples, and since many particles with a particularly large particle size are included, the surface area per unit mass becomes small, It is considered that the burning rate has decreased. In addition,
The EP suit has the longest ignition delay and is inferior in terms of ignitability, but the burning rate after ignition is petroleum coke and pellet 2
% And petroleum coke 98%.

Based on the above results, when the flammability of various samples was evaluated in terms of the time required to obtain a burning rate of 90%, petroleum coke (about 0.
3 seconds), a mixture of 2% pellets and 98% petroleum coke (approx.
0.32 seconds), EP suit (about 0.45 seconds), pellet (about 0.55 seconds)
I found that it would become longer in the order of seconds).

Further, although pellets using heavy oil as a binder are effective in improving the ignitability, it is expected that the combustion completion time will be long because large particles are easily generated due to aggregation.

The above test was carried out for an oxygen concentration of 21% (air), but it is generally said that the combustion reaction rate of a chain is proportional to the oxygen concentration in a linear manner. The combustion reaction rate of fuel can be increased.

[B] From the observation results of the particle structure of the flammable EP suit by electron micrographs (Figs. 2a and 2b), unburned carbon has a chain-like structure peculiar to vapor phase precipitation suits, and graphitized carbon. In the case of, the particles are laminated in a particle shape to form a structure like a lump of black pearls. From this, the unburned carbon in the EP suit is a so-called residual carbon type carbon that has poor combustion reactivity and is not structured, and the furnace temperature under normal boiler combustion conditions is 1100-1200 ° C. It has been found that combustion can be performed by replenishing an appropriate amount of volatile components or adjusting the residence time of carbon in the combustion chamber.

EFFECTS OF THE INVENTION (1) Currently, EP suits are disposed of as industrial waste for a fee, and are disposed of outside the factory or inside the factory premises.
Therefore, it is economical if the EP suit can be reused as a solid fuel according to the present invention.

(2) Boiler efficiency can be improved and carbon cost can be reduced by refueling by recovering and separating carbon.

(3) Since ash is removed from the EP suit, valuable metals such as vanadium contained in unburned carbon are also removed and recovered, so it is a good component of solid fuel.

(4) Since it is granulated, it is convenient to handle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the unburned rate (1-X) of various fuels and the residence time (t _R , seconds). In the figure, 1 ... EP suit, 2 ... pellet, 3 ...
Mixture of 2% pellets and 98% petroleum coke, 4 ... Petroleum coke. FIG. 2 is an electron micrograph of the particle structure of the EP suit, with FIG. 2a at a magnification of 100 times and FIG. 2b at a magnification of 6000 times.

Claims (3)

[Claims] 1. Particle size generated in the combustion process of petroleum hydrocarbons
Using a petroleum-based binder to granulate unburned carbon from an aqueous suspension of a mixture of unburned carbon and ash having a size of 10 μm or less, separate and remove ash, and use the resulting granulated product as a solid fuel. A method for recycling unburned carbon as a solid fuel, which is characterized in that 2. The method according to claim 1, wherein the granulated product is co-firing with another solid fuel. 3. The method according to claim 1, wherein the unburned carbon is unburned carbon generated in a combustion process of petroleum coke or a synthetic gas production process by partial oxidation of hydrocarbons.