Method for calculating minimum urea injection amount of marine low-speed diesel engine SCR system

Abstract

The technical scheme of the present application discloses a kind of calculation methods of minimum urea injection amount of marine low-speed diesel engine SCR system, define the emission value of nitrogen oxide of emission level two as A g / kwh;The maximum allowable value of nitrogen oxide of emission level two is Amax g / kwh;The emission value of nitrogen oxide of emission level three is B g / kwh;The maximum allowable value of nitrogen oxide of emission level three is Bmax g / kwh;When the urea injection amount of nitrogen oxide emission value of reaching emission level three is R L / h;The calculation method is as follows: the minimum urea injection amount under the minimum nitrogen oxide conversion rate is obtained by formula Rmin=[R*(1-Bmax / Amax)] / (1-B / A).Through calculation formula, based on the emission value of four loads (25%, 50%, 75%, 100%) NOx, maximum allowable value of emission and urea injection amount under the NOx emission value of reaching Tier3, the minimum urea injection amount required for four loads is calculated, whether diesel engine meets IMO Tier3 requirement can be conveniently judged by verifying whether the urea injection amount of SCR system exceeds the minimum injection amount on ship.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of diesel engine technology, in particular to a calculation method of minimum urea injection amount of a marine low-speed diesel engine SCR system. BACKGROUND

[0002] In order to reduce the pollution of exhaust gas emitted by the ship during navigation to the environment, a selective catalytic reduction technology (SCR) system is designed, and meets the international maritime organization (IMO) emission level three (Tier3) of nitrogen oxide (NOx) specification formulated by the revised MARPOL Annex VI and NOx Technical Code 2008 (NTC2008).

[0003] For a low-speed diesel engine with a rotating speed of 130 rpm, when navigating in an emission control area, the IMO NOx cycle value must meet the requirement that the limit value is not more than 3.4 g / kwh (emission level three Tier3); when navigating in a non-emission control area, the IMO NOx cycle value must meet the requirement that the limit value is not more than 14.4 g / kwh (emission level two Tier2).

[0004] The selective catalytic reduction technology system is a kind of system that through the injection of urea solution, the ammonia (NH3) produced by the pyrolysis of urea solution and the nitrogen oxide (NOx) in the exhaust gas are chemically reacted, so as to reduce the concentration of NOx in the exhaust gas, reduce the emission, and reduce the pollution to the environment.

[0005] At present, there is no method to define the range in which the actual injection amount of urea solution in the selective catalytic reduction technology is effective, reasonable and meets the IMO Tier3 requirement, and on the ship, only some other means (such as NOx concentration test) can be used to verify the satisfaction of IMO Tier3 requirement.

[0006] Therefore, it is necessary to define the minimum urea injection amount of the diesel engine selective catalytic reduction technology system, and it is beneficial to the inspection of the ship. SUMMARY

[0007] The technical problem solved by the present application is that there is no method to define the range in which the actual injection amount of urea solution in the selective catalytic reduction technology is effective, reasonable and meets the IMO Tier3 requirement.

[0008] To solve the above technical problems, the technical scheme of the present application provides a calculation method of minimum urea injection amount of a marine low-speed diesel engine SCR system, wherein,

[0009] Definition

[0010] The emission value of nitrogen oxide in the emission level two is A g / kwh;

[0011] The maximum allowable value of nitrogen oxide emission of the emission level two is Amax g / kwh;

[0012] The nitrogen oxide emission value of the emission level three is B g / kwh;

[0013] The maximum allowable value of nitrogen oxide emission of the emission level three is Bmax g / kwh;

[0014] The urea injection amount when reaching the nitrogen oxide emission value of the emission level three is R L / h;

[0015] The calculation method is as follows:

[0016] The minimum urea injection amount under the minimum nitrogen oxide conversion rate is obtained through the formula

[0017] Rmin=[R*(1-Bmax / Amax)] / (1-B / A)

[0018] The minimum urea injection amount under the minimum nitrogen oxide conversion rate is obtained through the formula

[0019] Optionally, the actual nitrogen oxide conversion rate N% is obtained through the ratio of the nitrogen oxide emission value of the emission level two and the emission level three, and N%=1-B / A.

[0020] Optionally, the minimum nitrogen oxide conversion rate Nmin% is obtained through the ratio of the nitrogen oxide emission value of the emission level two and the emission level three, and Nmin%=1-(Bmax / Amax)。

[0021] Optionally, Rmin=(R*Nmin%) / N% is obtained through the ratio of the urea injection amount when reaching the nitrogen oxide emission value of the emission level three / the minimum urea injection amount / the actual nitrogen oxide conversion rate / the minimum nitrogen oxide conversion rate.

[0022] The beneficial effects of the technical scheme of the present application are as follows:

[0023] The present application calculates the minimum urea injection amount required for four loads based on the emission value, the maximum allowable value of emission and the urea injection amount when reaching the Tier3 NOx emission value of four loads (25%, 50%, 75%, 100%) NOx, so that whether the selective catalytic reduction technology system urea injection amount exceeds the minimum injection amount can be conveniently verified on the ship to determine whether the diesel engine meets the requirements of IMO Tier3. DETAILED DESCRIPTION

[0024] The present application will be further described below, but not as a limitation of the present application.

[0025] The embodiment shows a calculation method of minimum urea injection amount of a marine low-speed diesel engine SCR system, wherein the emission value of nitrogen oxides of the emission level two is A g / kwh; the maximum allowable value of nitrogen oxides of the emission level two is Amax g / kwh; the emission value of nitrogen oxides of the emission level three is B g / kwh; the maximum allowable value of nitrogen oxides of the emission level three is Bmax g / kwh; the urea injection amount when the emission value of nitrogen oxides of the emission level three is reached is R L / h; and the calculation method is as follows:

[0026] The minimum urea injection amount under the minimum nitrogen oxides conversion rate is obtained through the formula

[0027] Rmin=[R*(1-Bmax / Amax)] / (1-B / A)

[0028] The minimum urea injection amount under the minimum nitrogen oxides conversion rate is obtained through the formula

[0029] In the embodiment, the actual nitrogen oxides conversion rate N% is obtained through the ratio of the emission value of nitrogen oxides of the emission level two and the emission value of nitrogen oxides of the emission level three, and N%=1-B / A is obtained.

[0030] In the embodiment, the minimum nitrogen oxides conversion rate Nmin% is obtained through the ratio of the emission value of nitrogen oxides of the emission level two and the emission value of nitrogen oxides of the emission level three, and Nmin%=1-(Bmax / Amax) is obtained.

[0031] In the embodiment, the urea injection amount when the emission value of nitrogen oxides of the emission level three is reached / the minimum urea injection amount=the actual nitrogen oxides conversion rate / the minimum nitrogen oxides conversion rate, and Rmin=(R*Nmin%) / N% is obtained.

[0032] The characteristics and functions of the present application are further understood through the following description.

[0033] According to the basic principle of SCR, it is known that:

[0034] The greater the urea solution injection amount, the more ammonia gas is produced by pyrolysis of the urea solution, and the more ammonia gas reacts with NOx (NOx is the general term of nitrogen oxides) in the exhaust gas, so that the concentration of NOx in the exhaust gas after the reaction is less, and the conversion rate (emission reduction rate) of NOx is higher. Conversely, the smaller the urea solution injection amount, the lower the conversion rate of NOx. The urea solution injection amount is proportional to the conversion rate, and inversely proportional to the concentration of NOx.

[0035] Therefore, the embodiment provides a new calculation method to obtain the minimum urea injection amount.

[0036] Under the same single load (one of the four loads of 25%, 50%, 75% and 100%):

[0037] i. The NOx emission value for Tier 2 is A g / kWh;

[0038] ii. The maximum permissible NOx emission for Tier 2 is Amax g / kWh;

[0039] iii. The NOx emission value for Tier 3 is B g / kWh;

[0040] iv. The maximum permissible NOx emission for Tier 3 is Bmax g / kWh;

[0041] v. The urea injection rate at which the NOx emission value of Tier 3 is achieved is RL / h;

[0042] The minimum NOx conversion rate is calculated using the following steps:

[0043] a) Obtain the actual NOx conversion rate N% by the ratio of NOx emission values ​​of Tier 2 and Tier 3; N% = 1 - B / A;

[0044] b) Obtain the minimum NOx conversion rate Nmin% by the ratio of NOx emission values ​​of Tier 2 and Tier 3. Nmin% = 1 - Bmax / Amax;

[0045] c) The amount of urea injected when the NOx emission value of Tier 3 is reached / the minimum amount of urea injected = the actual NOx conversion rate / the minimum NOx conversion rate, Rmin = (R*Nmin) / N;

[0046] Thus, the formula for calculating the minimum urea injection rate under the minimum NOx conversion rate is obtained:

[0047] Rmin=[R*(1-Bmax / Amax)] / (1-B / A)L / h.

[0048] in,

[0049] The NOx emission value for Tier 2 is expressed as the NOx value when the urea solution is not sprayed.

[0050] The NOx emission value of Tier 3 is expressed as: the NOx value after emission reduction by urea solution injection reaction;

[0051] The maximum permissible NOx emission value for Tier 2 is expressed as the NOx emission value under the worst conditions, meeting the IMOTier 2 requirements, and without urea solution being sprayed.

[0052] The maximum permissible NOx emission value for Tier 3 is: the NOx emission value after urea solution injection emission reduction under the worst conditions and meeting the IMO Tier 3 requirements.

[0053] The present invention will be further elaborated and explained below with reference to Tables 1 and 2 and specific implementation examples, but this should not be construed as limiting the scope of protection of the present invention.

[0054] Table 1 - NOx emission values ​​and maximum allowable emission values ​​for Tier 2

[0055]

[0056] Table 2 - NOx emission values, maximum allowable emission values, and urea injection volume required to reach Tier 3 NOx emission values.

[0057]

[0058] Taking 75% load in Tables 1 and 2 as an example:

[0059] a) Actual conversion rate N% at 75% load = 1 - 2.02 / 13.03 = 84.5%

[0060] b) Minimum conversion rate at 75% load: Nmin = 1 - 3.39 / 14.48 = 76%

[0061] c) Minimum urea injection rate at minimum conversion rate under 75% load:

[0062] Rmin at 75% load = [136 * (1 - 3.39 / 14.48)] / (1 - 2.02 / 13.03) L / h

[0063] =123 L / h

[0064] In summary, this invention, through the calculation formula for the minimum urea injection quantity, calculates the minimum urea injection quantity required for four loads (25%, 50%, 75%, 100%) based on the NOx emission values, the maximum allowable emission values, and the urea injection quantity required to achieve Tier 3 NOx emission values. This allows for convenient onboard verification of whether the urea injection quantity of the selective catalytic reduction technology system exceeds the minimum injection quantity to determine whether the diesel engine meets the IMO Tier 3 requirements.

[0065] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for calculating the minimum urea injection quantity of a marine low-speed diesel engine SCR system, characterized in that, definition The emission value of nitrogen oxides for emission level two is A g / kWh; The maximum allowable emission value for nitrogen oxides in emission category two is Amax g / kWh; The emission value of nitrogen oxides for emission level three is B g / kWh; The maximum allowable emission value for nitrogen oxides under emission category 3 is Bmax g / kWh; The urea injection rate is RL / h when the nitrogen oxide emission value reaches the emission level of emission grade three; The calculation method is as follows: Through formula Rmin=[R*(1-Bmax / Amax)] / (1-B / A) To obtain the minimum urea injection rate with the minimum nitrogen oxide conversion rate; The actual nitrogen oxide conversion rate N% is obtained by comparing the nitrogen oxide emission values ​​of emission level 2 and emission level 3, resulting in N% = 1 - B / A. The minimum nitrogen oxide conversion rate Nmin% is obtained by comparing the nitrogen oxide emission values ​​of emission level 2 and emission level 3, resulting in Nmin% = 1 - (Bmax / Amax). The ratio of urea injection quantity to minimum urea injection quantity when reaching the nitrogen oxide emission value of emission level 3 is equal to the actual nitrogen oxide conversion rate to the minimum nitrogen oxide conversion rate, resulting in Rmin = (R * Nmin%) / N.

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