Pengeringan pada pupuk dilakukan agar sifat higroskopisnya dapat berkurang. Terdapat banyak jenis alat pengering dengan aliran dan kondisi pemanasan berbeda, salah satunya adalah pengering putar dengan aliran secara kontinyu dan pemanasan secara langsung. Demi dapat selalu menjaga kualitas produk yang dihasilkan, dilakukan evaluasi kinerja pada alat, yaitu menghitung efisiensi, membuat model matematika, dan menentukan faktor yang paling berpengaruh. Hasil dari perhitungan efisiensi didapat nilai rata-rata efisiensi berdasarkan panas laten 32%, efisiensi berdasarkan panas laten dan panas sensible 32,3%, dan efisiensi berdasarkan penurunan suhu udara pengering 58,3%. Model matematika didapat dengan cara regresi linier ganda. Hasil membuat model matematika didapat dua model, yaitu Y1 = -0,0084852 + 5,546.10-7 X1 + 1,361.10-8 X2 + 0,0001399 X3 + 1,839.10-6 X4 dan Y2 = 44,74481 + 0,1248157 X1 + 0,0024587 X2 – 0,0005997 X3 dengan variabel terikat secara berturut-turut kadar air produk dan suhu udara keluar pengering. Faktor yang paling berpengaruh dapat ditemukan dalam model matematika yang dibuat, yaitu suhu udara masuk pengering.

Fertilizer drying is implemented in order to reduce hygroscopic. There are many types of drying equipment with different flow and heating condition, one of them is rotary dryer with continuous flow and direct heating. In order to take care of product quality, equipment performance evaluation is carried out, i.e. calculate efficiency, make some mathematical models, and decide the biggest impact factor. The result of calculating efficiency in average data are 32% for efficiency based on latent heat, 32,3% for efficiency based on latent heat and sensible heat, and 58,3% for efficiency based on decrease of drying air temperature. Mathematical models can be found by multiple linear regression. There are two results of making mathematical model, such as Y1 = -0,0084852 + 5,546.10-7 X1 + 1,361.10-8 X2 + 0,0001399 X3 + 1,839.10-6 X4 and Y2 = 44,74481 + 0,1248157 X1 + 0,0024587 X2 – 0,0005997 X3 with product moisture content and drying air temperature exit dryer as dependent variable. The biggest impact factor can be found from mathematical models that was made, there is drying air temperature enter dryer.

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